The Citadel's Survivor

Having survived the destruction of his own earth, Kim Hooper now resides on an earth similar to his old one. But there is one large difference. This world is filled with so-called heroes that fight against the monsters that brought ruin onto his own world and which stem from the countless dungeons and towers that litter this world.  Stuck in a similar-but-different world, he enters one of that world's most famous 'hero academies' so that he can fight against the creatures that killed his friends and family and ravaged his world. Armed only with the mysterious system-like power that saved him from his old world, he sets out to stop this earth from falling into the same fate that his old one did.   Heavily inspired by 'The Novel's Extra' at first.