Kin no Kanojo Gin no Kanojo

The plot starts when Ayanomine Erika, after meeting Yasuda Noborou one night, fell into a lake. The "Lady Of The Lake" appears and asks Noborou, "Did you lose your golden girlfriend or your silver girlfriend?" This leads to the original girl being split into two different persons: Erika, the golden-haired and Ginka, the silver-haired.