This is a low grade H manga pretending to have a story.
The isekai part is for to explain:
why the MC is confident
while his initial bullied loner personality is for self insert (For those who don't get it: This is how the manga industry views his main costumer base.)
This just sound like the ultimate horny introverted fantasy out there i came back form another world for sleeping with every woman who came on to me which is a lot for some reason.
I'd have more respect for this if it was just straight up porn.
Anyone unironically self-inserting themselves into this, life gets better but you have to actually try. Take regular showers, use deodorant, brush your teeth, get a nice haircut, learn a hobby, don't doomscroll, participate in bettering your community, seek real, tangible joy and learn to hold it in your heart.