Reimu Hakurei is the main protagonist in all of the main Touhou games and a recurring character in the spin-offs.
She is the Shrine Maiden of the Hakurei Shrine and she takes her job of exterminating youkai way too seriously. Sometimes she takes it to the extreme, beating up youkai that are on her way for fun. Her latest apperance was confirmed for Touhou 15: Legacy of Lunatic Kingdom.
Her most antagonistic role was in a fanmade game, Concealed the Conclusion. Also known as the "Lady in White", she serves as the final boss of the game where she prevents Marisa Kirisame from trying to save Gensoukyou from being destroyed.
She reveals that the world of Gensoukyou is in fact, a dream, and when she wakes up, everything will be destroyed - including Marisa herself.
Reimu is later fought in the Extra stage, with her colors restored.