Ever since Yukari became involved with a series of railway accidents. Things have not been the same in the Yakumo household. Tension rose between Yukari and Ran, the two fought over the morality of each others actions. Yukari yelled at Ran for telling Nitori how Yukari froze the points and how she let Flandre go. Ran yelled at Yukari for how dangerous her acts were. The two argued over if mechanical youkai were living things or just machines and just that. One day, Ran caught Yukari burning evidence that would prove that she was responsible and Ran told Nitori what had happened.
Just as Ran came back, Yukari interrogated her. The two were once again fighting. This was slowly getting to Chen, who watched the two Yakumos fight. The two were just about to bring out their spell cards, when they both heard a bang and a rip.
The door that went outside had a hole in it, with some broken furniture on the other side. The two checked if anything else happened, only to find that Chen was gone.
Chen was sad to leave Yukari and Ran, but her home was falling apart at the seams. She wanted to be in a place were she could be happy, so she wandered away. Not knowing if she'll ever come back.