Ren Elsie Jewelria female side. She has a huge crush on Rito Yuuki.
Run is a jealous, desperate girl that has declared herself the love rival of Lala (unbeknownst to the Devilukean princess of course). She is always ordering things out of the galactic mail order catalog to try and give her an edge... predictably, they never do. Either the device backfires, or hits Rito. Usually ending with Rito humiliated in one way or another.
Run has a rather small role in the anime, the show only focusing on her for one episode in a water park where she attempts to fish the swim suits off of the other girls to humiliate them (despite the fact that it really wouldn't concern Lala one bit). After she mistakenly fishes off Rito's shorts a couple of times, Run resorts to somthing more drastic, she unleashes a school of swimsuit eating pirahnas (only in ecchi manga).
Lala catches Run in the act and Rito, undertstandably, becomes angry. Run starts to cry and flees the area.
Anime: She gets harassed by a group of older men and Rito comes to her aid. Also, Run demonstrates a remarkable appatite, downing a huge amount of food inside of five seconds.
Manga: Run is approached by a talent agent and is offered the chance to become a singer. She happily agrees, seeing it as a way to snatch Rito's attention away from Lala. Her career skyrockets to the point where she is offered a shoot on a local tv show (ironically, one that Lala absolutly adores), Run then becomes very good friends with Kyoko Kirisaki, the star of the show who also happens to be an alien. Kyouko and Run become great friends because it turns out that Kyouko is an alien as well.
Run has the ability to have internal dialogue between herself and Ren, they always argue over who's turn it is to be the active persona.
Run never really makes any headway with Rito. She is an adorable girl though... if only she didn't turn into a guy every time she sneezed.
Now that Run's career as an idol has really taken off, she is usually the one who is conscious. Her talent agent, as well as other people who work for her, know she is an alien with two genders as they are aliens as well.Therefore they try their best to keep Run from changing to Ren during concerts.
In a recent chapter of To-love Ru:Darkness, Run has a deep heart-to-heart with Rito about how much she loves him but that she has no chance with him because of her male side, Ren. She then undergoes a transformation, which happens to all of her people when they reach maturity, that separates Ren and Run. This allows Run to enter into Momo's harem plan.
The planet that Run's species comes from is barren. A majority of the planet is desert that can't sustain the species life.