Naze Boku no Sekai wo Daremo Oboeteinai no ka?  

なぜ僕の世界を誰も覚えていないのか？, Why Does Nobody Remember Me in This World?

The original world was one where five tribes competed for dominance on land. this era ended with mankind's victory, led by hero sid. however, this world was suddenly replaced in front of a boy named kai. in the new world, humans lost to the tribal wars due to the absence of hero sid. dragons and demons now rule over the ground, and kai is forgotten by all human beings. after meeting rinne, kai decides to change his fate and break free from the rewritten destiny. despite there being no heroes in this world, he inherits their sword and martial art and takes on the powerful enemy races that reign supreme.