Nue Houjuu is a nue (a type of youkai analogous to a chimera) from Touhou Project. She was the Extra Stage boss in Undefined Fantastic Object, and the Extra Stage midboss in Ten Desires.
Nue is always playing malicious pranks, and is always hiding her true form. During the events of Undefined Fantastic Object, she decided to have fun by planting Seeds of Unknown Form in the fragments of one of the keys needed to free Byakuren Hijiri from her imprisonment in Makai, which made the fragments take on the form of UFOs. After Byakuren is freed, she learns that Byakuren is a friend to youkai and decides to join her at the Myouren Temple. Months later, after Toyosatomimi no Miko is resurrected, she calls in her friend, Mamizou Futatsuiwa, from the outside world as backup.
In M.U.G.E.N, Nue Houjuu has been made by various creators.
This version has gameplay and custom sprites based on the Touhou fighting games, so she uses only one button for melee attacks and has more projectile attacks than the average M.U.G.E.N. character, though the spellcard system works a bit differently.
Rien's version is closer to that of a more normal fighting game character, with a three-button layout. This version attacks primarily with her "wings" and trident, and her projectiles are UFOs that perform different actions depending on their color. Blue ones travel in one direction, green ones appear from above to fire a laser or move erratically, and orange ones mostly move in a direction, then teleport and change direction. Nue herself is also capable of teleporting, to help ease the trouble of her attacks being a bit clunky, and her supers/hypers are above average in strength. Some of them are capable of dealing exceptionally heavy damage if used properly, giving the character overall a very quirky feel. Her defense and life are lower than the average character, making her very fragile.
Her A.I. is quite weak.