Ok, this seems its off to a good start, although i would have gone a different way and had the entity merge both Gil and Emiya but leave Emiya as the dominant personality, essentially giving him all of Gils abilities, magic and knowledge of how to use his Noble Phantasums, would have been awesome, but still this is good, please continue i will follow!

Really, really, REALLY looking forward to seeing how this goes!

Ohhh my this is looking to be something interesting and I can’t wait to see what you do.

Ohhhhhhoho (laughs evilly) so Gilgamesh is here to I wonder how that will affect everything in the future

Good chapter but will Heracles appear soon or will he arrive later as he’s one of the characters that pulled me here when I was searching?

-
Muramasa closed his eyes. The salty air of the sea filled his nostrils. He remembered a strange client who came from china, a man who begged him to teach him how to forge the katana.
In exchange, he had learned a thing or two about chinese sabers, as well as some Chinese sword arts. While he was sure that his master exceeded him in martial skills as a whole, he was confident that his sword skills were unmatched.
After all, he needed to be downright proficient and sophisticated in order to forge the best katanas!
Mana spiked the air, the immense heat burning his core from a distance.
''Well, well, what do you think of that, Emiya?
''Hmm, I wouldn't be surprised if our 'invitation' was sent by a demigod of the sun. This reminds me of Karna.'' Emiya answered.
Muramasa's eyebrows shot up.
''You've met one of the most overpowered demigods of India!?'' he exclaimed, eyes filled with excitement. ''Did you see his weaponry!?''
Emiya mentally rolled his eyes.
''Yes, I've met him in another place, another planet. Yes, I saw his famed spear.''
Muramasa drooled.
''Can you show me a copy of..?''
''No. It's impossible to even replicate such a divine weapon.''
''Aww, too bad. Any tips around Karna?''
Emiya scratched his chin in his landscape.
''Hmm, I propose that you do not engage him in a fair fight.''
''Huh? Excuse me?''
''It's exactly what I've said. Do not try to confront him head-on.''
''Oooook? Care to explain?''
''Karna is virtuous yet very gullible in a certain way. When asked for help, he will help without a shred of doubt.''
''Reminds me of someone here.''
''He is far more extreme than my younger self. Coming from me, it means something.''
''Uh-huh. Right from his own legends, right?''
''Yes.''
''So, basically, you recommend me to exploit as much as I can, to turn his own righteousness against him?''
''...Yes.''
''As a certain friend of the hero of justice, I must decline.''
''Hmph. Try not to get yourself burnt to a crisp, old man.''
''Yeah, love you too.''

-
His skin was half charred by the heated air and his limbs were threatening to drop dead. 'Not a good condition at all', he thought. 'I need a distraction, an opening, anything!'
''Would you mind if I borrowed your katana?'' a voice spoke up. Before Muramasa could even ask why, Emiya took over his body control with unexpected ease.
Emiya screeched his body to a halt and propelled into the sky with bursts of concentrated mana. He shot through the night sky like an azure comet, his katana rattling with excitement as it burnt his palm.
Karna shifted into a counter stance; his body arched back to release his Noble phantasm. Shoujyou muramasa growled in return as mana accumulated within its blade, increasing its fiery glow to the point of self-destruction.
'Hey, Emiya. You're not telling me that you're gonna-'
'Brace youself, old man. Don't want you fainting over some heart-attack'
Karna inhaled, a storm of hellish fire contorting the very space as he threw his supreme weapon with unmatched grace.
''With this one strike I shall burn my foes- Brahmastra Kundala-(O'Brahma, curse my soul)!''
''In Death you shall burn, O'mighty ape of fire (Shoujyou Muramasa)!''
Even before the momemt Shoujyou Muramasa contacted Karna's spear, Muramasa knew what would happen. Emiya could be a real bitch if he wanted to.
Lo and behold, the art of overloading legendary weapons with arcane of extreme density, the art of destroying one's opponent in exchange for the weapon.
Broken phantasm, the ultimate strike in the form of blades.
Emiya had been expecting the ridiculous explosion, as well as the immense wave of destruction that would follow. With one arm he struck out, throwing the katana at Karna, the other arm already tracing up is defense.
''RHO AIAS!''
Transparent barriers in the form of pink petals expanded in front of his body, shielding him against the deafening roar of flames. Seven layers of legendary shields, owned by the mighty protector of the trojan war.
Karna's spear pierced through the raging havoc and hit the first layer of his shield. The first shattered like glass, and while the second managed to hold longer, it was still no match for the divine spear. The third, fourth, and fifth followed the same fate.
From the corner of his eye, Muramasa saw Karna hovering in the distance, an amazed look in his wide eyes. Sadly, he had no time to enjoy his hard-earnt satisfaction when he noted Emiya had traced a bow in his empty right hand.
''What the-are you crazy?!'' Muramasa shouted in his mind.
''It was a gamble from the beginning. Now that I'm sure Karna's spear won't reach the seventh layer, I have a little time to prepare for my surprise.'' Emiya nonchalantly replied.
'How in the hell are you gonna snipe him with our left arm occupied, you idiot!?''
Muramasa felt Emiya smirk omniously on his face. The smug chuckle that followed did not ease him at all.
''Say, have you ever tried sniping with a giant great-bow set on one foot?''
''Oh no, you're not seriously going to attempt-''
Emiya cut off Muramasa's question with a foot cast in the middle of the gigantic crimson bow, his right arm straining the iron strings. With a strenuous heave, Emiya pulled the string back with the sole of his foot that pointed towards Karna.
Muramasa felt his other leg crack under the enormous strain applied to it. A faint swirl of mana in his right palm materialized into a coiled sword that reeked of starving bloodlust.
Emiya position the arrow on top of the bow, his mouth set in a tight line. It seemed that Karna hadn't noticed their 'surprise' just yet. He seemed content at gazing into his shield with vivid interest, as if trying to figure out what it was.
Emiya's liped curled into a cruel grin. The 'arrow' contorted, becoming more coiled and sleek by every passing second.
''Sorry in advance,'' Emiya quiped. Muramasa felt a nauseous feeling build up in his stomach.
''Wait, this red bow...from Alaya's database, HOLY SHIT IS THAT ARASH'S SUICIDAL-''
Muramasa didn't get the chance to finish.
''STELLA HRUNTING! FALLING STAR OF THE BLOODY BEASTS!''
The heavy twang of the bowstring anounced it's departure as Emiya let go of the crimson streak of devastating destruction. The arrow let forth a devious roar that shook the heavens and earth as it bathed in its freedom, declaring its release with carnivorous power. Simultaneously, Karna's spear glanced off the last layer of Rho Aias with a thunderous groan.
Time seemed to slow as the divine spear soared past their powerless body that flailed through the air like a drowning man. The spear hit the surface of the churning sea and exploded in a vast column of steam.
Karna's mouth opened in shock at the sight of an arrow of tremendous power that appeared out of nowhere. He quickly opened his arms and released a blast of volcanic flames that rivaled a small nuke.
The night sky was surreally lit up by the divine sun that outshone the pale moon, as millions of citizens woke up in shock at the whitening sky.
The sea began boiling as millions of dead fish appeared on the surface, boiled alive by the tremendous heat.
''Hey old man, care to take a dip in the salty hot spring to heal our tortured muscles?'' Emiya suggested.
''I really can't tell if you're just masochistic or purely sadistic.'' Muramasa shot back with a tired tone.
''Depends on whether or not you call this body mine, because I think this body is made from your data.'' Emiya snickered.
''You sadistic brat.'' Muramasa muttered
''You should thank me that everything went according to plan.'' Emiya teased.
''Yeah, sure. Right until the point you thought it was a brilliant idea to use a mini stella to blast us into oblivion.'' Muramasa snarled.
Back in his mind, Emiya shrugged with a shake of his head.
''Hah. Old, obsolete, and senile men need the help of us young guys. Capiche?''
''...''
With those words, they sunk below fuyuki harbor with a big splash.
Muramasa sighed as they hit the dark ocean floor, or atleast he mentally sighed. They were sunk after all.
He remembered his talk, or more like argument, with Artoria from just a few hours ago.
''Maybe this was a shit idea.'' he thought with a tinge of regret.

Firstly: That's not what angra mainyu did in the first place. The author is probably referencing Fate/hollow ataraxia.

Secondly: Shirou isn't an edgy, emo, or angsty person. Even if Shirou doesn't go through the fire he's still a good and polite kid. Though he is a bit cynical and sarcastic. But that just adds to his personality.

In the Fate franchise it's best to look deeper into things, for you never know if they have a greater meaning associated with them.

There are a lot of deeper meanings in the Visual novel.

For example :
Archer 'Spared' caster in the UBW route because she hadn't crossed the line yet, she hadn't killed anyone, just put them into comas(and she might be useful later on in defeating troublesome Servants). Medea is smart, she doesn't kill the livestock straight away, she milks them first then allows them to recover to milk them some more. She's ''Evil'', not stupid.

So in a slightly twisted way(to troll his younger self), Archer was adhering to his Ideal much closer than the young Shirou Emiya. ''To save Everyone'' includes Caster right?

The reason he killed her later though was because he isn't irresponsible. If he enacted is plan of 'Killing Shirou' with Medea on the loose: it would end poorly for everyone, and as far as he knew Lancer was the only other servant still around other than Saber of course. If he had known Gilgamesh existed(or rather remembered) his choices would have been different.

So really when Shinji showed up with Gilgamesh, Archer was internally like (Surprised Pikachu face) he hadn't known about them, but he couldn't back down anymore, for multiple reasons:

1. He was low on mana.

2. Saber would come to her rescue, which would leave him alone with Shirou(Just like originally planned), and unlike him who was low on mana she could swiftly save Rin. It's unfortunate that his plan nearly backfired with lancer showing up since he went in Saber's stead.

3. After he saw Gilgamesh, He also had a new objective: Train Shirou(beat Shirou up) so he can defeat Gilgamesh later.

HF Archer:
In the first place Archer didn't happily give his arm to Shirou. He did it because it was the best way to deal with the situation. And if you think about it, Archer killed 3 birds with one stone.

He "saved" Shirou which would lead to them resolving the shadow problem, and in the end the arm would kill him anyway.

This’ll be great! Oh I hope for some Shirou rage moments where he becomes dark and uses Angra Mainyu’s power! Kind of like Naruto when he uses Kurama’s power back when it was Kyuubi style like in the early series where he gets pissed and he goes Kyuubi mode and starts kicking everyone’s ass. Shirou will get possessed by Angra Mainyu and he just starts destroying everything and mentally, physically, and spiritually scarring all of the survivors of his rampages by showing them the evil of humanity! You’d know what I mean since you’ve read My Ideal Academia as Angra Mainyu has obviously done something to Kirishima that has killed all of his “Manly” spirit. And Gilgamesh will just reck all of the heroes and villains that get in his way or annoy him. All For One, you better start praying and kissing his ass because if you even try acting all high and mighty towards Gilgamesh, he will DESTROY YOU! If All For One really pisses Gilgamesh off, Gilgamesh will just stop messing around and pull out Ea and Erase All For One entirely!

Whyyyyyyy!, Great till the end.

Noooo! I reached the end and I want more! I thought there was already more than one chapter, but I was wrong.
I really hope that you update soon.
Anyway, please keep up the great work!

I think you may be misunderstanding something: Archer did succeed in becoming a hero - he didn't succeed in saving everyone though. Or rather if he did succeed the timeline would be pruned as the Human universe of awareness(Alaya) doesn't allow for utopias/dystopias, it's gotta be balanced. So Shirou's wish of saving everyone(Eternal World Peace) was impossible from the start.

The holy grail taint

Q: Brainwashing Servants

So basically you're only managing that on your own Servants unless you're Velber/The Shadow or the like.
Yeah, Sakura has ridiculous bonuses.

Gil section said:

Takeuchi: For such a powerful character, he did lose to Sakura rather easily.

Nasu: Gil lost to Sakura so easily because he let his guard down. What’s a king without complacency, right? I think the biggest factor, though, was a simple question of their respective natures. Gil was pretty much invulnerable against Servants because he was the “Killer of Heroes,” while Dark Sakura was the “Devourer of Heroic Spirits,” which extends to Servants.

Takeuchi: Buuut … Gil acquired a flesh-and-blood body for himself, so doesn’t that mean he’s technically not a servant anymore?

Nasu: It doesn’t matter because he got his new body through the Holy Grail system, which means he can’t deny the power of Dark Sakura, who is a manifestation of the Holy Grail itself. On another note, Gil’s magical powers were off the charts in his flesh-and-blood form, so absorbing that level of power broke the dam and caused Sakura to fall apart.

Saber section said:
Saber Alter potentially showing up in other routes
Nasu: No chance. Saber wouldn’t go dark for just any reason. Saber Alter is exclusive to Sakura’s route. When I was working on the part of the scenario involving Saber Alter, Saber was dead to me. I had to keep telling myself that in order to make Saber Alter truly dark.
Takeuchi: After all, even having an enemy as a Master wouldn’t turn Saber dark.
Nasu: Even a Caster’s power isn’t enough to truly taint her soul to that degree. If a Caster were to ever fully steal Saber, she still would not turn dark.
Takeuchi: So the only way to get Saber Alter is for Sakura to taint Saber with the power of the Holy Grail.

Quite an interesting chapter. Please continue as you are able.

As for the chapter itself, I appreciated it for what it was. You don't need to change the chapter, either, except maybe to trim the fat, so to speak. Also, while it's important to listen to feedback, it's also important to stick to your vision. You know what you want to write, so stay true to that and be confident in what you've written. That's why we're here: to read what you've written, not to cajole you into writing what we want to see.

Xoxo

I'd like to think that in this timeline where Shirou decides to jump into the grail hole: Archer Re-contracts with Rin. Unless Rin already re contracted with Saber? hum hum...Anyways a solid chapter wonder how the next will be!