Truth behind the Bloody Mary incident

The mystery is solved by Suou! We all knew from a few games about the Bloody Mary ritual incident that caused various students to leave the school for "personal reasons". Suou thought it is connected with the Basquiat secret and it can lead to know more about why Mayuri is confined in the school therefore she investigate.
It's interesting to see Suou fighting with her own mind when she keep hearing the voice of her mother mocking her in every action with sentences like "she left you" "what's the point?" etc... It definitely doesn't paint her as mentally stable right now.

Turns out it all started when a teacher named Karasumori Midori wanted to help her cousin Akitsu to get in a romantic relationship with Yatsushiro. To do so she started spewing false info about the other students around Yatsushiro and even ended up writing a letter faking the writing. This, however, backfired when the difference in writing got discovered and ended up leaving the school right after. Akitsu also left on her own because she understood what happened. Suou also deduced that the teacher was probably in love with her own cousin too due to the pair items (like the scrunchie).

Dalia knew everything and kept silent because of the "seal of confession". Of course that's assuming we can believe her because her reaction to us mentioning that name made her do a very different face than the usual Dalia we know.

Full on soap opera material here, but I honestly still don't see how this connects to the mystery around Shion Basquiat. Suou thinks that Midori knew something connected to it, but her leaving made the secret go away with her. Now the hope is that she left some hints around that could help Suou solve the puzzle.