He was in the same school and year as Kei and Tako the canon protagonists.

As a second generation rich, He passed his former life at home, not really showing at school, witch saved him from the school massacre.

Having survived the invasion, he got angered by Sei's and Reika's death. 

Wanting to change everything, he started to work for Gantz's inventor and his company. 

He used Gantz's technology to teleport his brain in his younger body. 

After his arrival in the past, he will use his knowledge of the future and the new equipment, he will change the past to protect his friends and the world.

He still like his former life-interests as : Marvel, Starcraft, MMORPG, etc, but his revenge is more important, even if this interests can be seen sometimes.