Rainstar is mentioned by Tigerkit as the cat he's going to marry in Chapter 38. A bit later, Gleamstar finds him making out with her. Upon meeting Gleamstar, Rainstar sends out Hollyleaf to attack her. Even though Gleamstar insists she wants to join them, Rainstar doesn't believe her. When Gleamstar is saved, Rainstar gets angry and threatens to send out Featherpaw. Fluffykit is shocked because Featherpaw is his boyfriend. Rainstar doesn't care, as she flaunts her sexuality, even after Fluffykit accuses her of being a homophobe.
When Gleamstar switches sides Rainstar is skeptical of her but shrugs it off when Lakepool assures her it's fine.
During the battle, when the Tribe comes upon the scene, Rainstar and Lakepool manage to convince them to join the Dark Forest's side.
When Gleamstar destroys the evil cats, Rainstar is spared.
Rainstar is a brown she-cat.
- Rainstar is mentioned to be Tigerstar's daughter, and assuming that he didn't switch mates, Hollyleaf is Rainstar's daughter, making Gleamstar and Rainstar sisters.
Mother (presumably): Hollyleaf
Mate/(presumed nephew): Tigerkit
Sister (presumably): Gleamstar
Sister-in-law (presumably): Jazzstar
Niece (presumably): Firekit
Nephew (presumably): Fluffykit