Manga by author Yamazaki Kore - Status ongoing

Hatori Chise is only 16, but she has lost far more than most. With neither family nor hope, it seems all doors are closed to her. But, a chance encounter began to turn the rusted wheels of fate. In her darkest hour, a mysterious magus appears before Chitose, offering a chance she couldnot turn down. This magus who seems closer to demon than human, will he bring her the light she desperately seeks, or drown her in ever deeper shadows?

From MangaHelpers: Kanako is a young woman who is running an old book store. One day, a customer comes in who shares her taste in books. He's a teenager named Akio, and he and Kanako quickly find that their taste in books is only the first of many ways that they fit together well. Kanako immediately realizes she wants him, and soon blurts out awkward things, like proposals of marriage and cohabitation. Despite their different ages and their awkwardness, it seems like their relationship has the potential to grow into something beautiful.