Unidentified Flying Object
An Unidentified Flying Object or UFO (未確認飛行物体 （みかくにんひこうぶったい） mikakunin hikou buttai) is any anomaly appearing in the sky that can't be definitively identified or explained as a known phenomenon or object. Most scientific explanations say the objects may be weather balloons, aircraft, mirages created by weather or light phenomenon, astronomical objects, or simply hoaxes. Because of their nature, UFOs are a favorite paranormal phenomenon, which often say that they are flying saucers of extraterrestrial (alien) origin.
Unidentified Flying Objects in Touhou
UFOs are central to Undefined Fantastic Object, where there is a reference to them in the title, and the plot follows the player character chasing a "UFO" in the form of the Palanquin Ship. They are also a gameplay gimmick, wherein blue, green and red UFOs are essential to scoring and power-up collection. It is eventually explained that the appearance of the UFOs are a result of Nue Houjuu's obfuscation ability, using her Seeds of Unknown Form to disguise pieces of the Flying Storehouse (飛倉 Tobikura) needed to unseal Byakuren Hijiri, which appear to the characters as UFOs.
In one of Mononobe no Futo's spellcards in Hopeless Masquerade and Urban Legend in Limbo, Fate "Gate Opening for Catastrophe", a giant UFO crashes onto the second player while a chiptune version of Nue Houjuu's theme, "Heian Alien", plays.
In Urban Legend in Limbo, UFOs and aliens frequently appear in Mamizou Futatsuiwa's spellcards, such as Unidentified "Scrolls of Flying Objects" and *Let's Go Home Soon, Aliens!*.
- Wikipedia entry for Unidentified Flying Object