As you guys guessed this "friend" is no friend at all, he gets pleasure from taking things from others, stealing their lovers gives him the best, he torments MC because they were close from childhood and he developed that kink so far back, MC is just unfortunate to be that close to him.
He stole the girl, Noa, because MC commented about her before the isekia, BUT, it wasn't a good comment, MC found her vibes weird, but the bastard misunderstood it as him being in love, and he was never able to stole a girl from MC because MC was anormal kid and still didn't fell in love with anyone, the chapter doesn't make the reader understand that, I think it could have done so though with some more text bubbles.
MUCH MORE SPOILERS BELOW
The NTR guy knows to have a special ability, he can't control it well but knows it acts on touch, if he touches someone, no matter the gender, they will develop good feelings towards him, in the novel MC let it pass because of bad writing, the author made him deeply uninterested in this bastard ruining people lives left and right, he initially thought it was a weak charm, then realized it stacked, so the more contact the worse it got, MC had a ste sister that was very young when this mofo charmed her, making her go half insane and ruin their family, all because he found it fun, then there was a tomboy childhood friend, he took her too and converted her into a slut, sadly MC thinks they would have gone bad anyway and the charm didn't change their personality, it totally did (childhood friend started to dress and behave all girly for the guy, made a 180° from her original persona, then started to sell herself to afford stuff for him, then just opened her legs casually, if it helps digest it, she and MC were casual pals playing games in the park, not close at all, the fucker simply seen too much in it).
The asshole knew he would get hate from the stolen girls boyfriends, and somehow made so that some of the hostility got towards MC because he was "his friend", he even made the ex-step sis act badly and the tomboy insult him, he liked to torment MC for no reason, because one thing is stealing, one thing is the other shit.
Noa is a succubus, I don't recall if she was charmed but she got close to assface for a certain special trait he have, it seems that when he touched her it broke the charms he had casted, and when MC returned magical wave disrupted the rapist charm too, both lost their preys, of course recasting it is possible but...thanks to events deploying fast after MC return it doesn't happen.
The organization checking on superpowers did investigate NTR bastard, but they got charmed too and gave false reports, after the dispel they confessed, it seems like they could have sealed his power but or didn't do it or made a very weak one that then broke, anyway they reported him as low risk and no danger.
MC seals him, and I think even makes him impotent when the bastard suddendly remembered MC have a mother, for some separated reasons it seems like she had a spell on herself making her hard to recognize, so he only thought of attackign her when really focusing on something that would make MC feel down, the guy tried to call some of the girls he charmed for casual sex after but eeryone refused as it was fully dispelled, all of them were confused but mostly thought of having fallen in love with his face and finally waking up, is even revealed he have a micropenis and the girls loved doing it with him for the charm enhancing the pleasure just by being with him.
It was satisfating but unfortunately it makes clear the author was coming up with the story as the chapters came as MC sealed him with ease, could have done so from the handshake but decided to let him roam as it wasn't a threat to himself, ignoring how the guy was efffectively raping girls, ruined his family by brainwashing a young girl and making her go mental and then making random people harass MC, MC only seals it after the guy proclaims his next target to be his mother, all of this is excused with MC character being twisted from the isekai and not having a normal view of things.
The ex step-sis and the tomboy tried to get closer to MC later, but MC shoots them down heavily, super not interested and believes they were destined to go bad anyway, ignoring how corrupting a kid is easy, the charm broke them, the asshole clearly made them act that way and even adults were affected, even adults with training and barriers.
genderbend him and plap. Best solution
