Who Lives Inside Me

When I traveled to a different world, I thought I would be greeted by a golden finger and an invincible life. As a result, we witnessed a bloody disaster on just the first day. Although he can deal with mutations calmly, he is still not the strongest in the school. But until he understood what his talent was. "Second person" - there is another person living in his body. Is he the unprecedented genius, or is he the so-called second person? Who lives inside me...? Or am I living in someone's body...?