|Японское имя:||櫂 トシキ|
Although he has a cold and stoic personality, Kai is shown to be concerned with Aichi's development, especially after Aichi awakens the power of Psyqualia. Having previously witnessed the corrosive effects of Psyqualia on his former friend Ren, Kai attempts to dissuade Aichi from using Psyqualia by telling him he lacks true strength and then quitting the team. However, his words have the opposite effect intended, making Aichi grow more reliant on Psyqualia for strength. It is later revealed that Kai's true purpose for leaving the team was to train alone and grow strong enough to defeat Aichi, saving him from Psyqualia's influence.
In the second season, Kai loses his Kagero deck and instead uses a Narukami deck, which he still uses in the third season. During the second season, Kai temporarily joined New Team Asteroid. In season 3, Kai is a member of Hitsue High School's Vanguard Club along with Miwa, Morikawa, and Izaki.