First, there's
The Hero May Have Stolen Everyone From Me, but I Won’t Give Up. In the End, I Know I’ll Be the One Who Wins: the main character has a bunch of childhood friends, all girls and all in love with him. There's a ceremony where they'll find out their skills and whatnot, and at that moment a summoned "Hero" shows up, identifies the girls' skills as having some kind of connection to the Hero and makes them part of his party. He "lets" the MC be part of the party too. Thing is he has mind control powers and regularly takes any girl he wants to his bed, brainwashing them to adore and serve him. Additionally, the "connection" between the girls' skills and him gives him an excuse to "strengthen their bonds" regularly. The manga version isn't over, but according to the forums
there are several endings/paths, all but one having the "Hero" lose his powers through a curse by the Demon King, resulting in all the girls gaining full control again. Any brainwashed girl who was impregnated had her memory altered to lighten the burden, but this didn't happen to any of the CFs thankfully. Either way, before the Hero can be executed the girls go to his dungeon and do the job themselves, very thoroughly and brutally. In one ending the MC doesn't know the girls were brainwashed and rejects them. In one he knows and they all live happily ever after together. In the path where there is no brainwashing the "bug" that caused that guy to be summoned as a Hero is finally fixed, and the MC becomes the Hero instead, succeeding in the quest and having a happy future with his childhood friends (and the little sister of the would-be Hero who was the one who was supposed to be summoned in the first place).
Second, there's
Keikenchi. Also has the MC be a comrade in the "Hero's" party. In this case, the party consists of MC Thor, his two childhood friends Nei and Soara who grew up with him and loved him for ages, and Hero Thane and Lisa who moved into the village at around 12. Thor fell in love with Lisa and got engaged to her, but one day Thane and the girls sat him down and told him they wanted him to leave the party on account of his inability to increase his level no matter how he trains. Thor notices Lisa is wearing a new ring where her engagement ring should be, and that the other two also have the same ring. He attacks Thane in fury at having stolen his fiance and childhood friends and making up a dumb excuse to get him out of the way, only to be literally kicked out. Very shortly afterward it's revealed that Thane has a brainwashing power that showed up out of nowhere, that he'd been using it on Lisa for ages to sleep with her behind Thor's back and recently used it on the other two girls as well. After a while Thane gets rid of Nei and Soara for various reasons, and when Thor saves them and discovers the brainwashing he offers to break the spell, which nearly breaks them mentally. Both of them return to their home village for maybe a year to recover, come to grips with things, etc. As for Lisa, well...
Soara says she's secretly a traitor, and eventually this is revealed to be beyond an understatement. She's actually the young Demon King in disguise. As long as the Demon King lives a Hero will be found somewhere, so if she kills the one she'd found she'll just have an unknown Hero out there somewhere she doesn't know, and by the time she finds him he may become too powerful to stop. So instead, she decided to corrupt the Hero Thane. She seduced him and Thor simultaneously, agreed to marry Thor to infuriate Thane, then gave Thane those brainwashing powers (which don't work on her because she's too strong). Once things had gone for a while and Thane was thoroughly wrapped around her fingers, she convinced him to get rid of his true allies one by one so he'd have no one with him but herself and disguised demons. This way, she's able to keep him weak and isolated and completely helpless, right up until her true identity is revealed. While the story isn't over yet, it's been confirmed by those that have read the original that it does indeed end with Nei and Soara marrying Thor (along with several other girls).
