To-LOVE-Ru Darkness Series by Saki Hasemi

Momo is the younger sister of Lala, the alien princess who has long since been engaged to the human Rito in the pages of To Love Ru Omnibus! Although Rito's heart continues to waver between Lala and his first crush, Haruna, Momo finds herself unable to deny the feelings she has for the hapless human male... moreMomo is the younger sister of Lala, the alien princess who has long since been engaged to the human Rito in the pages of To Love Ru Omnibus! Although Rito's heart continues to waver between Lala and his first crush, Haruna, Momo finds herself unable to deny the feelings she has for the hapless human male. Instead of giving up, Momo attempts to surround Rito with a harem of beautiful women, all working towards urging him to marry Lala, become crowned as King, and as a result, be allowed to marry his entire harem - Momo included! For Mature Readers! less

MetamorphosisMomo wants to hook up high schooler Yuuki Rito with the girl of his dreams-but why stop there? She won't be happy unless he gets all the girls of his dreams. To make her “harem plan” a reality, Momo sets Rito up on a date with Run. There's just one small hitch: Run is a shapeshifting alien, who can turn into a boy at a moment's notice.

Lethal WeaponAmong all the lovely ladies surrounding Yuki Rito, the deadly assassin Yami has always been a breed apart–aloof, dangerous, and haunted by the secrets of her past. When one of Lala’s inventions goes awry, Rito and Yami have no choice but to spend a whole lot of alone time together. Has the time finally come for Rito to learn about Yami’s secret history?