Onda Serika♀

Aisaku's osananajimi. Her parents died when she was small and she was raised in an orphanage neighboring Aisaku's house. She is bright, gutsy, funny, and tomboyish but is pure as one can see from her prayers at the church. She has a huge bust, and the ability to have ridiculous fantasies that stun the people beside her. Lives together with her nii-san who works as the master of a cafe. It's pretty obvious throughout the story that she has feelings for him, but since our protagonist is very dumb, he doesn't notice it.

[Edited from a combination of Accany's review and Warum's review]