So for Queen's Blade: We can keep the idea of him entering the tournament, being the first male ever to do so. No one believes he can make it far yet somehow he did, through his own skills and determination, even when his back is against the wall. In the end, he won the tournament, becoming the first king, plus since he had helped the others during the tournament in one way or another and having grown fond of him, they wish to become his loving sluts, willing to serve all his needs and protect him from whatever may harm him.
For highschool of the dead: My character managed to obtain a helicopter, using it find any survivors. He would come across the group of main characters, helping them out in escaping the horde. He then flies them to an island resort he had been too before, a safe haven. They settle in, yet things may very well get hot in more then one way with him with these women around.
Highschool DxD: My OC is unaware of what he truly is, believing himself to simply be a human, yet unaware of the fact that he's much more then that. He starts attending Kuoh Academy, meeting Rias and the various girls of her peerage, they sense his power and, well, let's just say that strangely, they want him to join the group, becoming more seductive and shall we say, needy In wanting to please him, give him whatever he wishes.