Based on this headcanon:

Sometimes Armin has such bad dreams he wakes up and just kinda throws up. Jean gets him a glass of water and a cold cloth and give him his blanket for the night. Every once in a blue moon, The rest of the squad finds the two of them tangled in one bed but nobody really bats an eyelash.

Connie sometimes wakes up screaming and the group learns pretty quickly to go get Jean because he always seems to know what to say to get him to calm down. Krista doesn't cry or scream or anything but Jean comes to learn that she likes hugs so he makes sure to hug her before she goes to bed every night and hug her first thing in the morning.

Sometimes Jean hears Mikasa pacing out in the halls in the middle of the night so he'll go make her some tea and talk her ear off until she falls asleep and he has to carry her back to her room. Eren doesn't like to admit it, but he's thankful Jean puts in the effort to make sure Mikasa gets enough rest. Jean tells Mikasa that it's Eren that carries her back to her room, but she knows it's him.

Jean Kirschstein for unexpected Team Mom."
{Source - post/75123050175/i-like-to-imagine-that-jean-is-the-security}

Sharing a barracks room got old fast. It was plenty big enough, of course, with each squad member having their own nook and bed to sleep in, but still. Everyone complained, frequently, and loudly, about the fact they had to share, but it was exactly how Jean liked it. He could look after everyone this way, keep a close eye on them - even Corporal Levi, who didn't take well to direct looking after but seemingly appreciated (or tolerated) indirect care.

Like leaving a candle lit on their shared bedside cabinet. It was so no one stumbled around in the dark, that was what Jean said, how he sold it to everyone after that horrible night when he'd been woken up by Levi screaming in his sleep about the dark. He'd clawed at his bedding, his sheets, making noises Jean had never heard him make while awake. Of fear and pain. How anyone else had slept through it, he'd never know, but from that night on, Jean left the candle burning bright.

It was fortuitous, really. Barely a night went passed in the room of the Special Operations Squad when someone wasn't woken by a nightmare, a flashback to the worst moments their eyes had seen or their ears had heard, and Jean became attuned to it. He slept well, woke up feeling refreshed, but he was alert to his team mates like a mother is to her children's cries. It was a subconscious awareness of his friends - his family - and how they were feeling.

Armin had night terrors, worse than anything Jean had seen before. They were always the same; Armin's hand flung in front of him, rigid muscles held tense and tight, shaking with the effort, and Eren's name on his lips, sometimes quietly murmured, sometimes cried out with so much fear it made Jean sick to hear it. Armin sounded so desperate, so utterly broken by what he was seeing.

Jean would fall out of bed and, using the candle's light to guide him, pad quietly to Armin's side, perching on the edge of his bed so he was within arm's reach. Usually, calm words, quiet reassurance, tucking him back in and making sure he was warm was enough to relax Armin back to sleep, his dream-fears quietened down that yes, Eren was fine, he was the one snoring, remember?

But sometimes it wasn't enough. All the kind words and soft voices in the world wouldn't help at all. Armin would thrash and sob, usually throw up, and then cry harder because he'd been sick, and Jean would be there by his side. He'd brush his hair out of his eyes, clean him up, swap blankets with him, reassure him that he was okay, while Armin would cry, sniffling and snuffling against Jean's shoulder, and the others would lay there awake, listening to him and Jean's soft kindness.

Usually, they fell asleep all curled up like that. No one passed comment. In the morning, Sasha or Mikasa would gently wake the both of them, Jean wrapped around Armin to protect him from the nightmares that'd plagued him.

Sasha understood those nightmares. She'd suffered with night terrors since childhood, but being in the Survey Corps, seeing her friends and colleagues being killed and eaten to defend the city she loved, had made those night terrors all the more realistic and pervasive. She'd wake up crying, thick tears pouring down her face so her pillow was wet and her nightdress damp, and feeling thoroughly hopeless and helpless to defend herself.

Jean was always there, with a tissue held out gently to her, a genuine, kind smile on his face. He memorised statistics and numbers to reassure her with, that after the first mission their chances of dying dropped by a third, and after their tenth? That was a just 10% chance of passing. Wasn't that worth living for? Fighting for?

She'd agree that yes, it was worth it. She'd ask him what he thought the world was like, and they'd talk about rivers and mountains, cool streams and hot summers. Wide spaces with no walls surrounding them, closing them in and keeping Titans out. She slept soundlessly after that, inevitably, her dreams full up of images of the world beyond the walls and how beautiful it would be. Exactly how it should be, in Jean's mind, and when she told him about those dreams, he used them as fuel to power their imaginings on the next sleepless night.

Connie was easier to gauge - he came to Jean now. He knew there was nothing he could say that would have Jean run away. The others fetched Jean now any time Connie awoke in the throes of a nightmare or a memory, knowing Jean would know just what to say to settle him down again.

Usually, it was teasing. 'Why've you got me up again, Connie?' 'What is it this time?' And Connie would laugh and tell Jean the horror story his brain had concocted up, and they'd pick apart every bit. Well, how could a Titan get in and eat them all? Levi was like... Right there. Even Titans must know about him, surely. Besides, Jean was pretty sure that Connie tasted pretty gross, so any self-respecting Titan would ignore him.

It helped. It even, once, raised an almost smile from Corporal Levi, when one night the whole barracks had awoken to Connie's cries. Everyone had sat and listened to the story, the tales Jean had told him, had joined in on the jokes when they could, Eren had promised Connie that he'd sleep with an eye open, Armin had propped the window shut, and Levi had guaranteed that any Titan who believed their room to be an all you can eat buffet would be shown just how wrong they were.

Laughter helped Connie, but for Historia, it was hugs. She needed reminding that they were all still alive sometimes. Jean started it - a bear hug for her first thing in the morning and last thing at night, and of course upon a safe return from a mission. Sasha carried it on, and even Eren and Armin by the end of a month were sharing short, sweet hugs with Krista when she seemed like she needed a human touch.

Especially when she thought about Ymir. After Ymir's death, the nightmares were worse than they were as time passed. Historia remembered every single detail about Ymir's death; the Titan had smelled like rotten flesh, the sound its jaws made, like two planks of solid wood hitting each other, the way it had glanced her way as it had gulped down Ymir.

It had, hadn't it? She would lay there wondering sometimes. Did you die as soon as they ate you? Or did that come later, a creeping, slow death in a pressure cooker of blood and digestion? Historia tried to find the courage to ask Eren, but never made it. The thought haunted her, though, and she spoke about it frequently to Jean in those sleepless moments in the dark.

Eren was one of the hardest to settle. It had taken weeks to convince Levi to allow Eren to share their room, but Jean had persevered. In the end, he'd sold it by reminding Levi and Erwin just how important it was for them all to feel a part of a team, a family, and locking Eren in a basement wasn't conducive to that bond developing.

The first week? No one slept. Levi purposefully stayed awake, staring at Eren's form under the sheets with a look of nervous displeasure on his face. He'd been at least proven right on one account - Eren did have spectacular dreams. He threw himself around in bed, yelling, crying, and frequently sleep walked out of the bed and around the room.

Jean, once he'd convinced Sasha to stop screaming when Eren grabbed her in his sleep, led Eren back to bed and tucked him in, with everyone's eyes on him. It took a long time for Eren to adjust to sharing a room again, and even still, after he transformed, he would sleep walk and talk the following few nights.

Mikasa worried Jean the most. Countless nights he'd wake up to the sound of footsteps, startling awake, and he'd lay there awake and listen for a few moments. He'd creep out of bed and out into the hallway, where he'd inevitably find Mikasa, pacing the floor and thinking to herself.

They talked about everything. Their pasts, Eren, missions, their futures, their dreams. No stone was left unturned, no thought left be. Both laughed and cried outside that barrack room, and Jean would sit up with Mikasa until she fell asleep. He'd gently pick her up, and carry her to bed again, tucking her in, and when she woke up in the morning, he'd tell her how sweet it was Eren carried her to bed at night.

They both knew the truth, but somehow, the lie came easier.

And Jean? He went to Marco. Marco was dead - Jean was no fool, he understood that Marco was gone - but if he closed his eyes, and strained his memory, he could almost hear him. Hear that unerring belief Marco had in him, the advice he'd give him in that moment. He never needed hugs or water or a candle lit beside him, because he had all of that in his memory.