Okay, this is fucking weird, but I kinda love it. I so hope that this entire manga is just a huge rugpull by the author, who pitched a generic SoL rom-com in order to get approved, and now that he's serialized, he just hard swerves into dark battle seinen.
"So you see, Editor-san, this story is about a weak protagonist who loves this girl, but she has several personalities, and he has to win them all over in order for their love to blossom! It's like a harem story, but everyone wins!"
"Hm yes, Mangaka-sensei, this does seem nice and safe, I approve"
"And then he'll have to train his ki in a martial arts temple, and battle the bio-freaks sent by the mad scientist to recapture his love interest"
"Hm, what was that?"
"Oh nothing, don't worry about it"