"Let me explain: rin loved miku and rin tried to kiss miku. but miku pushed her away because she was engaged. Rin exchanged herself to become a boy which was len so that she could love miku. Then miku fell in love with len and just ran away with him. Then that angel guy you saw in the video was kaito and rin was his love so he came up and shot miku because of that."

 

"In the story Rin fell in love with Miku.Even though she knew it was forbidden she loved Miku,So Rin made a contract with the devil to turn into a human boy(Len).Later Rin's friend/person who has a crush on her? found out and got angry at Miku,and killed her.Then realesed the contract to make another wish to exchange her life for Miku to live again."