I fully realize cultures across the world are different, but sometimes I just can't help but wonder "What in the world is wrong with Japanese people?" This beginning makes no sense. First, why is it so hard for these authors to introduce a main female character close to the age of the main male character. I'm happy MC isn't another teenager, but his thinking process is very teenagery despite fighting the equivalent of a war in another world. This is one of my pet peeves with Isekai and/or Regression stories or Reincarnation stories where MC's mental age and experience carry over. These MC's who have lived 30-100 (or more)+ years would not be acting like teenagers, thinking like teenagers, etc. unless they forced themselves to do so in order to blend in.
Then there's the whole idea that he's worthless in the real world despite having magic and superhuman physical abilities. What? That opens up so many options for him. He could become a superhero (sure some edgelords will rant against this one), he could become a body guard, he could get into construction work as someone said in the chat, he could become a mercenary, he could become a world renown problem solver, rescuer, the top tier special ops one-man team who goes in and fixes problems without killing everyone or something (depending on his power level). Why is this dude working in a restaurant as a dishwasher? That seems severely forced just to padd the beginning with this melancholy. I would've appreciated it better if author just had him do some stuff with his abilities while keeping those secret and maybe having some PTSD from the other world's war. Instead we get this sort of teenage angst stuff of not properly fitting in society????? Along with the 16 year old girl trying to hump a 30+ year old man??? Author couldn't just make her 18-20ish or something? I always wonder that about the lolis, shotas, etc. Authors can't just make them older outside of kinks you'd see in the darker parts of the web? Really? And if you want to argue this story/genre is meant to appeal to a younger audience, okay, make MC teenager (remove the 10+ years of him fighting other world war, shorten it to less to keep him returning as a teen) now, keep the girl as a teen. Not that hard. C'mon.