Seeing a lot of complaints and negative comments in here about the MC and the story, so my response:
Let the author do what they plan on doing, they're not writing to appease or appeal to YOUR specific interests - they're writing what they think is interesting. If you want some toxic OP alpha fukboi with nothing other than looks, go somewhere else;
if you have an issue with a boy having the mentality of an older male because isekai, liking a girl his physical age because he's actually mentally in his 30s, go find another manga - honestly, it's a work of fiction and you shouldn't be berating anyone for something that makes some actual sense rather than taking issues with the ones that make NSFW art of someone like Kanna from Dragon Maid - who actually looks like she's 6 or 7, then you need new priorities in life.