In To Love Ru: Darkness, Rito Yuuki continues to struggle with his feelings for both his crush Haruna Sairenji and the alien princess Lala Satalin Deviluke. Lala's younger sister, Momo, develops a crush on Rito as well and decides to form a harem around him, hoping to secure her own position in his affections.
Momo enrolls at Rito’s school and covertly assists his various potential love interests, even recruiting new candidates, including the newly arrived alien assassin known as Konjiki no Yami, or "Yami." Yami delays her next assignment due to Rito. However, Yami’s sister, Kurosaki Mea, intends to compel Yami to resume her duties as an assassin.
To Love Ru: Darkness unfolds following the conclusion of To Love Ru, bringing in new female characters, new foes, and increasingly risqué scenarios.