He is one of the students from Japan who got involved in the summoning incident, and ended up in Tortus along with his other classmates. He is somewhat like the leader of the whole class, as most of the students look up to him. This is further enforced by him being bestowed with the rare job as the Hero.

Spoiler

In the After Story, Kouki becomes filled with immense guilt over his past behavior and actions which prompts him to drop out of high school and wander around Tortus, immediately taking on bounty jobs to kill monsters as an act of atonement to the point of recklessness.