NO MEMORY: Remember in the World

The protagonist, Kagerou You, a boy called by the alias "Spirit Behind" is told by a god that a dimensional hole has opened, so he'll borrow the boy's power. In exchange, the boy obtains an ability. If he's not remembered by anyone in his original world, then he'll enjoy everything in this other world. And he swears that he'll make everyone in this other world remember him. He resolved to do so. However, that world is a world of swords and magic—that much is fine. But surprisingly, the boy's ability doesn't activate at all. An ability he doesn't even know how to activate, his power is on par with a high schooler, a level where he'd lose to ordinary monsters. Suddenly, he's enslaved by a thief. Can he survive this tumultuous other world?