Gray Maiden

Tsutako, Age 26, Stalker. Tsutako Kagami works in an office by day, and follows Azami Li, the man she's loved for over 20 years now, by night. One day, while she's stalking him as usual, Azami is hit by a car that immediately flees the scene. When she visits him in the hospital, it is apparent that he has amnesia... the perfect chance to have her every wish granted. She tells him, "...I'm your girlfriend, Azami." What will happen in this thrilling mystery, as her lie begins to spread out into consequences with those surrounding her and Azami...?!

(Source: MangaPlaza)