This is those chapter where author turn their main character into stupidly OP character with near limitless mana and strong sword shit, despite having trouble in casting some type of magic a few chapter before.
Without undeoing any training or power up
The author ruined his own story with these BS. If he's this strong then why the fuck he's doing nothing in the hero party? To the point that his former team members even thinking that he's weak. It just doesn't make sense.