MC accidentally ends up with a card that makes it seem like he is extremely powerful due to its grade/the rank it means when he is actually the weakest when it comes to magic, he slowly develops his magic ability whilst trying not to get caught and be revealed as a fake because it would get him kicked out the school.

MC starts of as a weak and timid human in the series in a school of monsters and has to hide the fact he is human but due to various events people thing he is actually really strong however as time passes and events unfold the MC becomes extremely overpowered as he slowly undergoes changes with his body.

He is just extremely lucky and because of that everyone thinks hes the strongest