東方星蓮船 ～ Undefined Fantastic Object is the twelfth official game in the Touhou series.
Undefined Fantastic Object features three playable characters (Seiga Kaku, Reimu Hakurei and Yukari Yakumo), each with two weapon types.
The UFO system works like OTL.
During the early springtime in Gensokyo, some few strange flying objects appears in the skies and later, a large flying ship passes by. Seiga, seeing this, gets suspicious and she invites Reimu, and Yukari to check out what's up. So either one of them actually decides to go check it out.
The first person they run into is Nazrin who basically tries to stop them in their way. Later, as they get closer to the flying ship, Kogasa Tatara appears from out of nowhere and manages to startle them. Upon her defeat, Kogasa kindly leads them to the flying ship. As they begin to board the ship they run into Ichirin Kumoi who tries to stop them as well, but lets them pass.
Once Seiga, Reimu, or Yukari meets Minamitsu Murasa, Murasa tells the story; most of the enemies in the game are trying to free Byakuren Hijiri from a sealed sleep of a few hundred years. Most of them collect the UFOs within their own reasons, though Seiga, Reimu, or Yukari eventually unseals and fights Byakuren herself.
Later, Seiga, Reimu, and Yukari finds out that Byakuren and her followers maintains a few Buddhist temples around in Gensokyo. However, Seiga's suspicion gets to her and she wants to find out what the UFO objects really were.
Soon, Seiga, Reimu, and Yukari later meets Nue Houjuu, who reveals that she was the one aiding and obstructing both sides during the quest. She also had scattered the Tobikura around discussed in UFO forms, and apparently wanted to start some kind of conspiracy theory of UFOs as she heard it from the Outside World...