Daughter of Akito's adoptive family and also his fiancee.
Arisa is a genius, despite being only 12 years old, she has already graduated from a famous university, and her essay is on multiple famous professional magazines. She is also good at house chores.

At the end of the 4th novel, she moved in to live with the Student Council members. While most of the Student Council members prefer to say that the engagement doesn't count due to her age, Akiko is the only one that views her as a love rival. However, after an argument of who is better for Akito, the two worked together as they noticed that Akito sees both of them as his sisters. She has a habit of going silent and showing emotions on her face, which is so cute that people who see it can't resist accepting her will.

(Source: Wikipedia)