A student at Enoshima Yonchuu Junior High School before coming to Tsujidou, Tsukai was a member of the 'Shitennou' (Four Heavenly Kings, meaning the strongest guys at the school). He has a crush on Yui Itou. Tsukai is a strong fighter, and often has to overcome harsh odds to win, but always seems to come out on top.

Spoiler

He was also a kouhai of Kunito Nakajo

Spoiler

Later in the series Yui Itou becomes his girlfriend

Spoiler

In GTO: Shonan 14 Days, he still hasn't stopped being a biker along with Katsuyuki.