Momo Belia Deviluke

Two cosplayers dressed as Momo at Comiket in 2012 (left) and Tokyo Game Show in 2014 (right).

As the daughter of King Gid and Queen Sephie of Deviluke, an alien planet far distant from Earth, Momo, the younger sister of Lala Satalin Deviluke and twin of Nana Astar Deviluke, holds the title of "Third Princess of Deviluke", as she is the youngest of the three sisters. Since childhood, Momo and Nana always argued. Whenever they fought, Lala would always found ways for the twins to reconcile and for Zastin (Lala's personal bodyguard) not to be angry with them. At some point in the time before the events of the series, Momo travelled through the galaxy and met tons of plants from different worlds, befriending all of them due to her ability to communicate with them.

Momo, alongside Nana, makes her first appearance in the manga in chapter 97 of To Love Ru, in which the twins arrive on Earth and transport basically the entire cast of the manga into a RPG world inside Trouble Quest, a virtual reality game that Momo and Nana programmed and used to determine whether Rito Yuki is worthy of being engaged to Lala or not.[3] In the end, after everyone exits Trouble Quest, the twins apologize to Lala for all the problems they caused before returning to Deviluke.[5] A few chapters later, they went back to Earth after escaping from Deviluke and their studies. However, they forgot that Zastin was also staying on Earth, who was instructed by their father to bring the them back home. In the end, they defeat Zastin and his assistants, and convinced their father that they're going to stay on Earth with Lala.[6]

During Momo and Nana's stay at the Yuki household, they created their own house in the attic using space distortion technology. They also take care of all their necessities to avoid disturbing Rito's younger sister, Mikan Yuki, for cooking, cleaning, etc. However, they still come down sometimes to eat Mikan's cooking. Throughout the series, Momo gradually develops affectionate feelings for Rito despite him being the fiancé of her sister Lala. She often fantasizes perverted situations with Rito, and desires for him to become sexually active towards her. Momo would constantly sneaks into Rito's room to sleep with him, sometimes even half-naked, revealing Momo's lustful side. Whenever she's asked of the situation, she simply says that she accidentally gets into Rito's room while she's half asleep. Momo has also stated that she knows Rito would not reciprocate her feelings, and that she's content just to be a lover. At the end of the series, in an attempt to confess his love for his classmate and longtime crush Haruna Sairenji, Rito fails and, instead, his confession is accidentally directed to Momo and three other girls.[7]

In To Love Ru Darkness, Momo takes over the role of the main female protagonist alongside Golden Darkness. Wanting Rito's love, but unwilling to cause conflict between Lala or Haruna, Momo realizes that if Rito becomes the next King of Deviluke, the laws of Earth will not apply to him, allowing Rito to create a harem where she can display her affections openly.[8] To accomplish this, Momo organizes the Harem Plan (ハーレム計画, Haremu Keikaku), a plan originally proposed by Lala to ensure that each and every girl who is in love with Rito can marry him.[9] The first phase of the plan is for Momo to enter Sainan High as a student so she can monitor Rito and the female characters closely, while the second phase is to turn Rito into a "carnivore" so that he would take it upon himself to create a harem. To do this, Momo manipulates various circumstances involving Rito and the female characters so that they end up in a romantic situation.[10] So far, herself, Lala, Haruna, Nana, Mikan (despite being Rito's sister), Darkness, Yui Kotegawa, Run Elise Jewelria and Rin Kujou are part of the Harem Plan, with Saki Tenjouin, Risa Momioka, Mio Sawada, Mea Kurosaki, Kyouko Kirisaki, Tearju Lunatique and Sayaka Arai under consideration to be part of the plan but, it's still unofficial as to whether or not they'll be part of the plan in the end. As of the present time, Momo's Harem Plan is gradually taking effect as Rito, who initially rejected the idea, is slowly beginning to consider it.

Throughout the manga, Momo continuously tries to find ways to make every girl around Rito fall for him as part of the Harem Plan. She would sometimes buy love simulation games as part of her research for the plan, which she uses to set the mood for him and a certain girl he's with or even when it's her. She hopes that one day Rito might return her love as well as the love of every girl who has feelings for him. After her mother, Sephie, comes to visit them, Momo hopes she doesn't find out about the Harem Plan, but after a brief moment with Rito, Sephie quickly realizes that her daughter is not only planning a harem for Rito but also hoping to be a part of that.[11] Much to Momo's shock, Sephie tells her that she's fine with Momo trying to get what she wants as long as her heart is fine with it.[12] Ever since her talk with her mother, Momo has expressed doubts about whether she would be satisfied with the Harem Plan. Most notably, when she learns that Rito and Haruna accidentally kissed each other, instead of becoming happy and enthusiastic like she would whenever Rito gets development with the other girls, Momo becomes worried, restless and uneasy; she feels like a loser, much to her own surprise.[13] Despite this, she pushes Rito to finally confess to Haruna. When Momo watches as Rito and Haruna's attempts to confess to each other once again went nowhere, Momo somehow feels relieved. However, after Lala reaffirms her own love for Rito and satisfaction in receiving love from him despite his love for Haruna, Momo also reaffirms her own satisfaction to receive his love and restores her resolve to resume the Harem Plan.[14]

In addition to the anime and manga, Momo has appeared in four To Love Ru video games: To Love Ru Darkness — Battle Ecstasy,[15][16] To Love Ru Darkness — Idol Revolution,[17][18] To Love Ru Darkness — True Princess,[19][20] and To Love Ru Darkness: Gravure Chance.[21] Momo also makes a cameo appearance in the third chapter of the manga adaptation of the light novel series Mayoi Neko Overrun!.[22]