"To Love Ru: Darkness" is a romantic comedy and harem anime that serves as a sequel to the original "To Love Ru" series. The story centers on Rito Yuuki, a high school student whose life becomes increasingly complicated due to his interactions with various alien girls. The narrative expands on the relationships and dynamics introduced in the first series, with a particular focus on Lala Satalin Deviluke, the alien princess who initially proposed to Rito, and her younger sister, Momo Belia Deviluke.

Momo takes on a central role in "Darkness," orchestrating a plan to create a harem for Rito, believing it to be the best solution to resolve the romantic tensions surrounding him. Her efforts lead to numerous comedic and dramatic situations as she attempts to bring Rito closer to multiple girls, including Haruna Sairenji, Rito's longtime crush, and Yami, a former assassin with a mysterious past. The series explores themes of love, jealousy, and personal growth as the characters navigate their feelings and relationships.

The plot also introduces new characters, such as Nemesis, a shapeshifting alien with a connection to Yami, and Tearju Lunatique, a scientist who shares a striking resemblance to Yami. These additions further complicate the story, adding layers of intrigue and conflict. The series balances lighthearted comedic moments with more serious undertones, particularly in its exploration of Yami's backstory and her struggle to reconcile her past with her present.

Throughout the series, Rito remains the focal point of the romantic entanglements, often finding himself in awkward and compromising situations due to his kind but indecisive nature. The interactions between the characters drive the narrative, with each episode contributing to the overarching themes of love and self-discovery. "To Love Ru: Darkness" maintains a blend of humor, romance, and occasional action, appealing to fans of the harem genre while expanding on the established lore of the "To Love Ru" universe.