Nene's childhood friend who also has experiences in stage performances. His hobbies includes creating inventions and showing them to Tsukasa. One of his notable creations is RoboNene, a Mikudayō-lookalike robot with an appearance similar to Nene, made specifically to assist her in stage performances. During middle school, Rui was once a social outcast, and many others looked down at him due to his intelligence, although he did manage to make friends with Mizuki Akiyama.