Kimiko Kujo

K whose real name is Kimiko Kujo is one of the letters of Wammy's House in L: Change The WorLd, who went down a dark path and became part of a bioterrorist organization which plans to "cleanse" the world of its excess population by a deadly virus.

She is one of the letters who went evil much like Beyond Birthday.

She is not in the anime or manga she is only in the film L: Change the WorLd