Watashi no Tadashii Oniichan

There's nothing in the world Rize likes more than to curl up in her warm bed and doze away—just like she used to with her big brother when they were kids, before they were separated by their parents' divorce. Working late shifts at a supermarket while attending university, she dreams of someday finding and reconnecting with her lost—and now grown-up—big brother. Her penchant for being able to nap in the break room draws the attention of Kairi, a co-worker who struggles with insomnia. Something about him reminds her of her big brother, and she finds herself growing closer to him...but when she discovers his secret, her whole world will be turned helter-skelter.

(Source: Kodansha USA)