保科 啓

The protagonist's classmate and Ayaka's younger brother, the youngest of the three Hoshina siblings.

He is the step brother of the two older siblings, his mother remarried and is the second wife of the father of the protagonist and Ayaka. He attends the same academy as the protagonist.

Unlike his sharp-looking older sister and brother, he inherited his gentle mother's traits and has an affable personality.

He looks much younger than his actual age, and combined with his airheaded nature, he is often teased by those around him (especially girls).