If you're looking for manga similar to Akuma Hakushaku no Hanayome: Shiroki Otome to Akai Kajitsu (Light Novel), you might like these titles.
Kanzaki Kaito is an otaku highschooler with no friends. Deriving joy from just conversing with online girls whom he did not even knew the face of, he passes his days in solitary. But, with his father’s remarriage, he suddenly became family with the top beauty of the campus, Momoi Saki, and her gentle and busty little sister Momoi Sakura! Sakura instantly got cozy with him, but Saki totally despised him. Then came one day, where the daughter of a big financial conglomerate, Saijou Kirara got ahold of Saki’s weakness and threatened her. Noticing something off about her sister, Sakura turned towards Kaito for help. Will the loner and otaku Kaito be able to save Saki!?
From classmates to brother and sister, living under the same roof. After his father’s remarriage, Asamura Yuuta ends up getting a new stepsister, coincidentally the number one beauty of the school year, Ayase Saki. Having learned important values when it comes to man-woman relationships through the previous ones of their parents, they promise each other not to be too close, not to be too opposing, and to merely keep a vague and comfortable distance. On one hand, Saki, who has worked in solitude for the sake of her family, doesn’t know how to properly rely on others, whereas Yuta is unsure of how to really treat her. Standing on fairly equal ground, these two slowly learn the comfortable sensation of living together. Their relationship slowly evolves from being strangers the more the days pass...