Despite the situation being dire, a sense of camaraderie had developed between the soldiers during their training. Even those who vowed to keep their distance, like Ymir.
You were different. Special. Perhaps it's the fact that back before she got turned into a Titan, she'd never actually known happiness. She survived, sure. People worshipped her in desperation. But she was never actually loved for who she was.
Right now, as she lies down on the lower bunk bed next to you, so close she can count your lashes, she realises that she feels happy. That she might just love you.
"Oh, yeah, and then I just gave him a bloody nose." She snorts, keeping her voice a hushed whisper if only to not get tattled and scolded by anyone. Her face brightens when she hears you stifle a giggle. "He cried like a baby." Ymir likes this. Feeling like it's just two in your own little world.
Part of her feels undeserving for your attention. You're everything, and she is... Ah. Though, she shouldn't get carried away and take this for granted. It'll be taken, just like everything else.