When Will You Rest? {FNAF & KNY Crossover}

It had been a normal day in Afton's hell. William was taking a break since Cassidy was preparing something special. Meanwhile, Cassidy was preparing to let William go from Ultimate Custom Night to another universe to start over.

When Cassidy tells him this, William was surprised. The vengeful child was letting him go. Actually, letting him go. She did warn him, however, that if he was to go back to his old ways, Cassidy would get involved.

William became Muzan Kibutsuji and everything was calm for the first couple of years. Then... William/Muzan got sick and began to experiment. When he turned into a demon using the Blue Spider Lily, he wanted to go further and further. He wanted to become even more immortal.

This caught Cassidy's attention, and she knew that she had to get involved. Cassidy became Yoriichi Tsugikuni to stop him. Although Cassidy/Yoriichi was neglected by her new parents, she took the time to begin to plot how to bring William back to UCN. Even after her twin was turned into a demon and even after her death, Cassidy would not leave this world until William was taken back to hell.

Nothing would stop her until justice has been served for her mistakes.

And, maybe, she would get a new twin brother in the process.