I loved this episode! It really did show a different side to Zenitsu, like you said, it made him so much more than just the comic relief. I also loved when he talks about his 'happy dream' where he is powerful and can help people not knowing that in that moment he was really living that dream. Also Zenitsu's teacher isn't actually his grandpa, he just calls him gramps because as he said in the episode he loves him :)