Mutsuura Rin

A classmate of the main character, she is the most conspicuous member of the gal group.

She had never spoken to him before, but at the school festival, she seemed to like an accessory he had made, and suddenly became friendly and aggressive.
The protagonist is bewildered, but happy to be relied upon, and continues to make expensive materials and provide accessories in response to her unreasonable requests.
Perhaps because of this relationship, they have become such good friends that they can call each other by their first names.