園崎 魅音 Sonozaki Mion
Mion is the oldest kid in Keiichi’s class and the leader of their club. Her social skills equal and rival Keiichi’s and she is often shown viewing him as her rival. It is later revealed that she actually has a crush on him.
Mion acts like a tomboy most of the time and calls herself oji-san which means old man. She is often showed carrying a holstered air soft gun which she never uses. She is also next in line to be the head of the Sonozaki family.
Mion is the only character that has never been affected by the syndrome and driven to madness.
Mion’s real name is actually Shion as she was born second to the Sonozaki family. Due to her sister swapping early on in life, Shion was mistaken for Mion and branded with the Oni tattoo causing her to choose to stay Mion forever.