Also known as: イリア(西方Project), Iria
The Tri Stars are a group of sisters called Tolia (Seihou) (トリア toria), Ilia (イリア iria) and Felia (Seihou) (フェリア feria) and are the third stage boss of Banshiryuu. It's unknown who's the older and younger one between Tolia and Ilia, but Felia is the youngest among them. Tolia is smart (but a coward if she isn't protected), Ilia is a scientist and Felia bluffs when she says she can see the future.
During the scenario, they have a warp device that allows people to teleport them. The heroine wishes to use this in order to easily get to Mars, but they won't allow them unless they rented, so they end up fighting. After their defeat, they send them to an unusual place, where they meet VIVIT-R or Hirano Sakurasaki, depending on the player's character. On the later versions of the game, the battle ends with a huge explosion.
https://en.touhouwiki.net/wiki/The_Tri_Stars