Y/N is a recent transfer from a run-down orphanage to Wammy's House. However, there's something she doesn't know: she's L's biological daughter. L sent her to that orphanage when she was a baby and observed her through security cameras to check if she possessed the deductive and cognitive skills necessary to succeed him. The only ones who know this are Watari, L, and Roger. Currently, L is deciding between Mello, Near, and Y/N to be his successor. L desperately wants to tell Y/N that she's his daughter, but he can only do so if she becomes his successor. Despite her cold demeanor, she's still his daughter, so he loves her.
Y/N and Mello were dating at Wammy's, but all changed when L died. Mello leaved Wammy's and let Near succeed L, but he didn't said goodbye to Y/N or even said he was leaving to her. That was always his biggest regret. He wanted to have warned her, kept in touch, or even taken her with him. Every single day, he wonders where she went, what she did with her life. However, neither Mello nor Y/N know that Y/N is joining the American mafia today.