I'm not sure what's happening to the MC here.
He doesn't seem to plan out any potential future confrontations caused by his earlier ones. He knew that he would likely be facing stronger opponents and yet he has nothing for the time being in-between testing new techniques. Like he had no tactics for the boss coming for revenge. A horrible death was highly likely with no interference from the fiance.
Then instead of being calm and understanding, he recklessly pisses off his girlfriend's mother with his attitude.
Was he this immature before he ascended into the fairylands? He acts like a bratty teenager thinking he's cool.
That latest fight could have been avoided if he asked questions instead of blindly threatening without even knowing how powerful the boss was.
It's another time he could have been killed because he is being increasingly reckless. He's acting more of a moron, it's no wonder he's losing more.