He won the 32nd Akatsuka Award for his debut work UNdeadman which appeared in "Monthly Shonen Jump" magazine and produced two sequels. His first serialized manga was his comedy "Angel Densetsu (Angel Legend)", which appeared in "Monthly Shonen Jump" from 1992 to 2000. His epic saga, "Claymore", appeared in the magazine from 2001 to 2014.

In his spare time, Yagi enjoys things like the Japanese comedic duo "Downtown", martial arts, games, driving, and hard rock and metal music, but he doesn't consider these actual hobbies.