Tsuyoshi Kikawada is a third-year high school student, seriously injured in a motorcycle accident two years prior, forcing him to repeat a grade and impacting his academics. Classmates often fear him due to his delinquent demeanor, though this perception is incomplete. He holds a deep connection with Yurio Mizukami, whom he regards as his "angel" for assisting him after the accident. This act established Tsuyoshi's profound loyalty towards Yurio. Their relationship becomes complex when Yurio confesses he secretly rigged Tsuyoshi's motorcycle before the accident, attempting to create a situation to befriend him. This revelation occurs after Tsuyoshi temporarily vanishes due to Yurio losing a puzzle battle against the Sphinxes. Despite the betrayal, Tsuyoshi forgives Yurio, strengthening their bond.

Preferring action over intellectual pursuits, Tsuyoshi aligns with his academic difficulties. However, he demonstrates reliability during dimensional battles, stepping in to solve a critical puzzle to rescue Yurio after the latter is consumed by a Sphinx, highlighting his capacity for quick thinking under pressure. Tsuyoshi transforms from a solitary delinquent figure into a protective and integral group member, valuing friendship and loyalty above initial appearances or past conflicts.