Third-year middle school student Yu-yu Kondo lives in Kanazawa city of the country of Kaga. Being unable to reject requests, Yu-yu often gets caught up in his sister's hobbies. When Yu-yu could no longer bear it and ran away from home, he was saved by Megumi Okura. Megumi invites Yu-yu to the Night Amusement Park "Wonder Hill" where her friends gather. The amusement park is where many youths of the Vanguard-centric group "Team Blackout" gather. And this is how Yu-yu encounters Vanguard and was drawn in by the appeal of Vanguard and the world and friends he had never seen before.
