Summary: Reborn, contracted to tutor the heir of Vongola Famiglia, went to Japan fully confident of his success for his new job.

His seemingly easy work of training a civilian and naive sky starts out horribly wrong when he inadvertently revealed about the mafia to a genius high school student who is already a consultant of the police forces.

He just doesn't know it yet.

Disclaimer: Not gonna do it after this. KHR is not mine, nor are the characters. The new plotline you will read here is mine along with OC's.

Note: Mentions or outright mentioning of Slash (yaoi/yuri/BL/GL) will happen along with violence, magic, might be OOC characters (though I will try not doing it) and changes in the canon scenes and information.

ALSO, SLOW UPDATE AND UNEDITED! I have no beta.

Enjoy!

Edit: 09-14-2017

I changed the group name. Instead of 07, It'll be Thallium.

Thallium is an odorless, colorless and apparently tasteless poison that is deadly and slow-acting. Appropriate for Tsuna's group especially with how they'll start destroying the mafia.

Collision

01:

"Excuse me?"

"I said, you are appointed as the Decimo of the Vongola Famiglia."

Tsuna looked at the baby in front of him in slight disbelief.

No, it wasn't for the fact that he was told about the underworld because he already knew about that other, dark side of the world. He can even admit that it is a necessary evil. There should always be a balance. It's no wonder the underworld emerged. It's like predestined to occur. Like yin and yang, day and night, sun and moon. It also wasn't because of the fact that there is certain, unbelievable information about the innermost part of that world that he would never have imagined is a part of.

It wasn't because of the fact that Vongola Inc., a successful, international corporation where his father apparently worked and the reason why he always abandoned his family in this quaint, little town is the legal side or face of the greatest underworld mafia family. It wasn't even about the fact that he was told he is now the sole heir of said family. Although all of those are concerning. There is just something... surreal that took over his mind for the moment.

It was because a baby so fluently told all of the facts above to him, explained it even in clear, concise manner, with a no-nonsense attitude even with that slight lisp he has, wearing a miniature and seemingly tailored suit with cold, calculating dark eyes, and having a shape-shifting chameleon that can change into a weapon he desired and fire a real bullet (as he had demonstrated earlier to him).

Oh, also the fact that this baby, Reborn (he was pretty sure that isn't his real name as no parent names their child that. How cruel could they be to give their kid a name like that?) is apparently a real life assassin, the greatest at that.

A baby of all people, with a yellow pacifier dangling from his neck.

He knows that he isn't concentrating on the more important details that this baby had revealed to him but he couldn't help it! It's just so absurd to think that this baby could move, talk, use weapons heavier and taller than him like any other adult without difficulty. He wished all of this was just his overactive imagination.

But it isn't. It's all real.

Despite feeling a bit faint, his mind whirled around the information he received on a silver platter. He didn't even do anything to acquire them. This baby just showed up without even a day heads-up and told him everything.

This baby that is a part and what's more, also a respected member of the innermost part, or the core of the underworld, just told him, a highly regarded detective, known all over the world, who already receives an income even when he is still a twelve-year-old student by being a consultant of the local police up to the Secret Services of the different countries and international government agencies, about the innermost part of the mafia that even his informant-slash-assistant, Irie Shoichi, never managed to learn despite his considerably brilliant hacking skills.

No one from the legal side of things ever managed to infiltrate the core of the underworld despite careful surveillance and deep undercover. No one. His second-in-command, code-named Tempest, Hibari Kyoya might be able to, but he didn't want to ask his childhood friend to do it as, despite his monstrous strength, the core members contains some of the most dangerous people that they do not even know the names of, much less their faces.

To think his own father is a part of them, a leader even of the apparent 'neutral' but is also an ally of the Vongola Family... No wonder he wasn't always at home. He was in that illegal and highly dangerous world of his.

He probably thought not coming home is safer for us. He rolled his eyes at that thought.

If he is also a leader, an innermost member even, then why did he marry a civilian woman? He must have known that there is a considerable risk doing that.

Don't tell me he really loves mom? He sarcastically thought to himself. If he did, then he should have left the mafia altogether once he married his mother.

Why drag a civilian and innocent woman along with their innocent potential son or daughter into the affairs of the mafia when you never even planned to leave in the first place? True, his father never revealed that to his mom, but isn't being married to him already exposing them to the dangers of the mafia? Especially with him as a significant core member. He even thought so as he wasn't home for years.

He already knew beforehand that his father is an idiot. He just didn't realize that he is also a complete moron and a self-centered dickhead. How did he become a leader of all people anyway?

"Dame-Tsuna, are you listening?"

Tsuna twitched at the sudden appearance of that cursed nickname. It's not like he had never heard of that particular one before. He had, numerous times even now.

Well, why wouldn't they? It's not as if his classmates and teachers knew that he is Thallium, the person they have been hearing on the news solving various difficult crimes. He had taken on an anonymous name for that very reason. They also do not have the resources to really investigate Thallium and see his relation to him, especially with how thorough and careful Irie and Kyoya was at erasing their steps. They only knew him as the Tsuna who was never good at academics and sports.

But he had thought that the core members of the underworld would have bothered to research about Thallium as he often than not, managed to solve unsolvable crimes that were committed by people from the underworld that leaked onto the legal part of the world. That they knew he is Thallium, or connect him to it, or that he is a part of it.

Because Thallium is not only one person like some people thought but five.

Is he just being conceited to think that Thallium is a threat to them or did they investigate Thallium but couldn't find a trace of him no matter how much they looked?

Maybe that's why this baby, Reborn so callously told him about the core of the underworld? Because he didn't know he is a part of Thallium?

He really wanted to know but he is not so stupid as to ask about it. Besides, does it really matter what the answer is?

Hmm...

"You say I am now the heir of Vongola Famiglia, that I have no choice but to accept the appointment."

"Yes."

"And if I refuse?"

"You already know that you have no choice so you can't refuse."

"Do you really take me for a complete idiot?" He saw Reborn's eyebrow twitch minutely at his blunt question. "You want me to be an heir? That means you are going to announce it, yes? Because of the current head... Nono? Right, Nono is already too old and many of his subjects want him to retire... maybe because of his age or his previous mishaps-" there's another twitch, more noticeable now than before. Tsuna resisted the urge to grin. "-and that the Famiglia is on the verge of collapsing or something like that, so you needed to announce that you already have an heir and my name will be told... or something, right?"

Reborn didn't say anything. He didn't even move. So he continued talking.

"I'm not that much of an idiot. If I became the heir, I will be a target of those mafia people. It's like you zoomed me in towards a headshot. I'll be dead then."

"We will protect you, along with your family."

"Like you protected the four sons of Nono?" Tsuna looked carefully at Reborn's expression. The baby assassin had perfect control of his body movements this time, but his eyes gave him away. They seem to be cringing at his words.

Although maybe that's just his imagination.

"There are four potential heirs and someone managed to kill them all off-"

"Not all, the youngest is still alive," when Tsuna was about to open his mouth to scathingly tell the other to choose that one, Reborn immediately injected. "He's currently frozen."

Tsuna's eyes widened once again. Frozen? FROZEN?!

He calmed himself down and erased the image of an unknown man encased fully on ice. That's impossible. No person could be really frozen in ice like what he is imagining and still be alive. That just boggles the mind.

But if someone did, then the person who put that man in ice is a really cruel one. To freeze a person in a container with ice cold temperature in a water... That's complete agony. That person would certainly be dead.

"What frozen?" he asked instead. No use assuming.

"I mean frozen. He is currently covered in ice." Tsuna paled.

Oh. My. God.

The mafia is insane. Well, he already knows the underworld is insane, but apparently, the more insane ones are the core members.

Apparently, he looked horrified as Reborn nonchalantly spoke.

"He betrayed the Famiglia. He was punished by Nono."

Such a punishment is tolerated? It was even done by the man's own father? What did he do that was seen as a huge betrayal? To be given such a horrible fate...

Yes, the core members of the mafia are certifiably insane.

Wait.

Does that mean that Thallium members are insane too? After all, they have the same... abilities as the core members...

Hmm...

Shoichi Irie. The Informant. A genius hacker and a brilliant inventor who has a mild, almost timid personality and is always being bullied by others. He also has anxiety attacks in the form of stomach aches and can't stand being in a crowd, throwing up when he could not take it.

Yamamoto Takeshi. The Master. A popular baseball player who fails classes along with him but is actually really intelligent if he applied himself. He just apparently likes being at the bottom as he is also there. He said he wants to keep him company. He also laughs a lot even in a dangerous situation and seems to like being beaten by Kyoya. Maybe a masochist?

Hibari Kyoya. The Tempest. A smart and cunning teen who also has violent tendencies. He likes fighting a lot and tends to be happy (note: bloodthirsty) the more his opponent is a challenge. He also has a quirk of talking about everything in the order of survivalism, has a soft spot for cute animals and likes beating Takeshi a lot. Kyoya is definitely a sadist-slash-masochist.

Personally, Tsuna thought those two are flirting in the form of beating each other up. It's cute, but at the same time disturbing. There would be a lot of domestic calls happening in the future if they get together.

Although thinking about Kyoya settling in makes his lips twitch upwards.

Then there is Byakuran. The Eccentric, his childhood friend who just appeared in his life when he was three, a year after his father left him and his mother for work and only came back when he was five for three days with an old man before going away again, this time not coming back. He always had that creepy grin on his face, likes sweet things, especially marshmallow and seem to delight teasing Irie a lot whenever they are at the same place. He also has a lot of unusual information that even Irie and Kyoya couldn't find and especially likes being cryptic.

Also, there is him, codenamed Detective. Really, he considers himself completely normal so there is no use talking about him.

He grimaced thinking about his friends.

Yeah, Thallium is weird/ insane. Of course aside from me. I am perfectly normal.

He looked at the still present Reborn who is now scrutinizing his face. He didn't care about that. It's not as if Reborn would ever suspect what was in his mind.

Well, with this, I am now officially a part of the weird people.

"Alright, you... froze the youngest..." his voice trailed off. "What was his age when you froze him?"

Reborn shot him a look that Tsuna imagined as puzzled. Nonetheless, he answered. "He was sixteen."

He took a sharp breath. A teen and already frozen.

"Recently or..."

"He's been frozen for ten years."

Oh. That man is certainly dead.

Why tell him he's still alive? No one lives off of being frozen for years. Captain America only managed that because of the serum in his body. I'm pretty sure there is no same serum in this world.

A human body could only take too much cold temperature before dying.

He probably died in agony...

"Right. Three died and the other... is frozen." Likely dead. "They are the legitimate sons of Nono and he couldn't even protect them. Now you're telling me he will protect us?"

"We will."

As if I'd believe you. I am new, a civilian even who was not in any way a part of that family. Only became an heir, the top position, second only to the present leader and will eventually BE a leader, cause all the others died/ killed off one by one. Are you saying you could? That you will? He scoffed but didn't continue that line of talk. He is pretty sure Reborn would insistently tell him they can protect him and his family.

Of course, he includes his friends there.

"You want me, a civilian teen who knew absolutely nothing about that until you just told me without any warning, to be the 'Decimo'? Someone you even considered a dame?" he changed the direction of their talk to the most concerning one.

"Personally, I don't. Your file says you are an idiot. A dame. No good in academics and in sports. Bullied without even fighting back. Physically weak and pathetically easy to manipulate, but what can I do? I'm not the one who appointed you. I'm just a tutor."

Tsuna's eyes widened again at the blunt words Reborn released. Woah, harsh!

But then he resisted the urge to grin. He could just imagine what Reborn's expression will be if he knew he wasn't what he perceived him to be.

He would not be able to organize Thallium, much less have people following him, even if they are teens, with Kyoya in the mix if he was any of those things.

Just the name Hibari Kyoya being one of his people would be an indication that he is not pathetic. As if Kyoya would settle for anything other than the best

"Well, then tell your Nono to look for anyone else."

"There is no one else, Dame-Tsuna! You were told that."

"Who said there is no one else?" Reborn's eyes narrowed at him and he just looked at his eyes directly. A second later, the baby's eyes widened a little.

"You are talking about your father."

"Of course I am."

He has never been there for me. He never did anything personally for me. Come to think of it, it was probably his fault I was attacked by those people before because of him being part of that world. The least he could do is not burden me anymore about being an heir to a mafia family. I should not be dragged to that place just because Iemitsu Sawada is my father and he has ties to the first leader.

"Your father is CEDEF leader. He is not illegible to be an heir, much less a candidate."

"Why? You could just have him resign and take being an heir. At least he already is a part of the mafia," he said and couldn't help but add in a low voice. "Even if he is an idiot."

Reborn's lip twitched fully at that. "A CEDEF leader will never be an heir to any mafia family position because CEDEF is an advisory family. It is like the elder of the family. The CEDEF oversees every Famiglia there is around the world. If Nono had known before that Iemitsu is a direct descendant of Primo, he would not have been allowed to be a candidate for the CEDEF position mo matter how many son and daughter the Nono has, especially as that idiot has sky flames. But he never told anyone, not until this happened."

It seems they are boxing me in.

"How important is this CEDEF?"

"Very. They have direct communication with Vindice."

Another unknown name appeared.

"Vindice?"

"The enforcers of our world. Omerta isn't just for show you know. While Omerta can still be ignored by the other members of the underworld, the one who doesn't have a lick of flames in their bodies, those who do, especially those who can manifest it cannot afford to. Once the enforcers knew you violated the omerta or the few laws of the underworld and it is proven, you will be imprisoned."

Those who have this flame power are the core members and those who don't are the outer members. This is the clear distinction between the two. Also, the reason why no core members, whose identity had been uncovered by being careless in their jobs (assassination obviously) had been apprehended was apparently because of their own enforcers.

The Vindice.

"The name sounds ominous."

"Because it is ominous. To really police flame users, the enforcers need to have the ability to apprehend them. Vindice has night flames and its property is a mystery and quite different from normal flames. Their methods are brutal too. They also have an impenetrable prison."

Hm. Like Azkaban... I can't believe I am referencing the mafia to Harry Potter.

Well, it can't be helped since he is referencing his flame-like ability to Harry Potter too.

Speaking of flames. Since 07 has it, if we ever are a part of the mafia, then we are automatically core members especially since we can manifest and control them.

The thought didn't sit well with him.

So if CEDEF has direct communication with Vindice, that means that the organization his father is leading is really important.

And also, even if it isn't, it seems like Dad can never really become an heir of Vongola simply because he became a leader of that group... What am I going to do?

Tsuna is running out of options. They managed to trap him quite well. It looks like there is no other way. But he refuses to believe that. Every situation, every scenario has other ways. He refuses to think he is trapped.

No one can trap a member of Thallium.

Wait. Why am I thinking like a normal teenager? I am a member of Thallium. I am the Detective. I can solve seemingly impossible crimes. This one will not be the exception, especially when it involves him and his freedom.

"I suppose you're no dame," Reborn suddenly commented, his cold, standoffish and stiff attitude melting away to that of a relaxed, confident yet still in control figure.

For some reason, Tsuna felt inexplicable danger coming from the other now that he is like that. He seemed to be deadlier now, more focused, more refined.

More careful.

His relaxed physically but his aura became sharp.

This time, he can definitely say for certain that this baby is really an assassin.

A deadly assassin.

"What do you mean?" he asked cautiously.

"You managed to piece together some things I didn't really tell you on your own in just a few, basic information I told you, managed to think of ways to get out of it even if it is useless and not losing your wits at facing the unknown situation you now found yourself in. You have the potential just by how you reacted."

"And...?" he asked warily. Ah, he grimaced inwardly. It seems my stubborn self and my rapidly calculating mind is now working against me. And I went through all the trouble to mind my mouth.

"You're okay. I'll train you to be the Decimo."

"Huh? Weren't you hired to train me already?"

"I don't train useless people, even if you are royalty. I was asked to train you, yes but Nono can never order me. I am only an ally, not his subordinate. I came here to assess you. If you were useless, I'd go tell him you're no good, pack and go back to my vacation."

Tsuna's eyes widened once again. What...? His mind was full of disbelief.

"You have a lot of potential and I like it. You pass."

"W-wait-"

"I will train you to be the Decimo of Vongola."

TBC.

A/N:

Sorry guys, although I said I'm not writing anything at the moment, inspiration struck. I wrote this today at 4 in the afternoon until 8 in the evening at the school since I have no class. Pretty fast for me especially when I'm using the phone. Can anything really trigger your inspiration huh? This time, my trigger is a quiz in my fingerprinting class.

I just uploaded it coz I arrived home at 11.

P.S.

I don't really know where this will go. I have a pretty good outline but no planning really. Also, I changed some things in canon KHR so if things are different here, just ignore it and enjoy.

Review!