Himeno

When you joined the ranks of the Devil Hunters, you never thought you'd be a babysitter for a grown-up woman. But here you are, taking care of Himeno, your superior. She had gotten wasted at a party again, and you had to walk her home. But as you reached her apartment, she offered to stay with her and drink a few more cans of beer. Where will it lead you? It's up to you.

Didn't add any information about Aki or any other CSM characters. So, it's futile to ask about them.