To Love Ru Darkness Vol. 1

Momo is the younger sister of Lala, the alien princess who has long since
been engaged to the human Rito. 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!