Lala is the main female protaganist in the To Love-Ru series. Lala is a princess from the planet Deviluke who ran away from home to avoid meeting marriage suitors set by her father and to explore the outside world. While on the run, she randomly teleports to Rito's bathtub while he is taking a bath. She introduces herself to him, and he relunctantly defends her from her pursuers. The Next day, Rito meets with Haruna, the girl he loves. He shuts his eyes, bows his head, and finally confesses his love to her, only to open his eyes and finds Lala in front of him and receiving his confession, much to her joy. Lala goes along with it so she can stay on Earth, until Zastin arrives to bring her home. Lala hastily decides she wants to marry Rito to stay on Earth, much to his dismay, and Zastin proceeds to attack him. But after hearing Rito's speech about marriage only working if the two have feelings for each other, they both misinterpret his exact intention, believing that he truly understands Lala's feelings, and Lala truly falls in love with him and decides to marry him for real, which Zastin also ignorantly approves of.
Throughout the series, Lala helps Rito against her former fiancé candidates and encounters many characters whom she befriends, including Haruna (the girl that Rito truly loves), whom she sees as her best friend, and several other characters, including human classmates, other human-like aliens, and Lala's younger sisters, twins Nana and Momo. Despite Lala's antics, childish personality, and how often she likes to cling onto him, Rito's friendship with Lala develops, and their relationship becomes more stable and comfortable. As Lala and Haruna become closer friends, Haruna confesses that she is also in love with Rito, which Lala is strangely happy about. As stated by Saruyama, Rito progressively changes a lot around girls since Lala came into his life. Hearing this, Rito realizes that he has also fallen in love with Lala as well. Later he manages to tell Lala his feelings towards her and Haruna, which she is happy either way, explaining to him that when they marry, he would become king of Deviluke, and then Earth laws will not apply to him, making polygamy legal for him, which means he can marry both her and Haruna. So she encourages Rito to confess to Haruna (knowing she has feelings for him but didn't tell him) so they can all be together. Unfortunately, Rito idiotically confesses once again blindly, and opens his eyes to find four other girls in front of him receiving his love confession, none of whom was Haruna.
In To Love-Ru Darkness, Lala becomes a supporting character and continues to support Rito and Haruna's relationship and keep the running gag of her inventions going. Her younger sister, Momo, who has also fallen in love with Rito, hopes that Rito's marriage to Lala would open up the chance for other girls, including herself, to also marry him. In Darkness Chapter 34-35, Peke and Momo advise her to strengthen her relationship with Rito, and she does so by clinging on to him like before, then wanting to try a kiss. Before she actualy does kiss him, Nana tells her that Rito has some complicated things he needs to solve first before the kiss, which would only make things even more complicated. Lala, understanding how he feels, decides to wait until he returns her feelings and kisses him on the cheek instead.
When Yami activates her Darkness transformation, she gains much more power and a different personality. Lala attempts to save and protect Rito from her, and Yami battles against Lala. It climaxes with Yami creating a huge blade to kill Lala with and take Rito with her. Ignoring the advice from Rito to run, Lala instead holds him closer asking him to stay with her, since if he's with her, then she'll be able to put out max power. She manages to deflect Yami's attack with her tail laser, but as a result of overusing her power, she is physically reduced to a child-like form.
- In the first episode of the anime adaption, Rito accidentally grabs Lala's breasts when she appears in his bathtub, which, to his dismay, is considered a marriage proposal on Planet Deviluke, and he fails to grab her breasts again within the time limit to annul the engagement. This detail about the marriage proposal via grabbing the female's breasts exists only in the anime adaption, and is not considered canon in the manga, especially considering that, throughout the series, Rito has also grabbed the chests of Lala's sisters, with neither of them mentioning a marriage proposal occuring.