Shijima Mei/Synopsis

The Melancholy of the New No.3
Shijima Mei appears at the end of the arc, being revealed by Tsukasa as a present for Mitsuba. She is seen crying and cowering under a table in fear.

Picture Perfect Arc
Shijima Mei was first noticed by Yashiro Nene after cleaning the pool. She appears to be drawing flowers in her sketchbook behind the fence. Shijima then disappears from sight. In the tower, she tells both Kou and Nene to kill Mistuba and Amane to escape. After Nene was taken by Hanako and imprisoned, Shijima checks up on Nene before getting threatened to make a deal with her. This eventually leads to Tsukasa showing up and granting her wish. He grants her wish to kill herself, the original, before she finishes or submits the tower that will create her. It fails because of Nene's inference with Mei.

End of Dream Arc
Shijima Mei was originally tied up by Kou before escaping and doing the same to him. She participates in the plan with Mitsuba, Kou, and Nene to escape the fake world before its finished. She tells Nene to go to No.1 for information that may help with her short lifespan, in addition to offering her sketchpad with her yorishiro to undo the fake world. She was seen talking to Tsukasa after the fake world is destroyed, and the two discuss in the art room about the payment for the wish she made.