Finding the last boss at the end of the "beginner's village" arc.
Well, it does happen in some games, but it's still pretty rare. Fighting him right away occurs even less often.
In this case, the MC is unlikely to win by himself, but his father and "onee-san" might make a difference.
But what happens after that if they do win?
"Congratulations to me, I saved the world. Now what? Going to look for the love of my (previous) life and seduce her without the circumstances that got us close in the first place?"