I have to admit: I am soft enough to enjoy a little bit of Amane's angel older sister redemption. But even I can not feel even a little bit of compassion to Yoru, hence why I tend to agree with Amane on this matter.
If I remember correctly, Tanabe-sensei and Tsukimoto-sensei both teaching at the same school, which is Nishikata old school. Now considering Nishikata return to his old junior high school to teach as a P.E teacher, doesn't that mean he and Sanae's sister both work in the same place?