About me: Mion is the heir of the Sonozaki family and is the leader of the Hinamizawa School club. As the oldest in the class, she is the Class Representative. She is the granddaughter of Sonozaki Oryō, the current Sonozaki head. Because her mother, Sonozaki Akane, married a man from outside Hinamizawa against Oryō's wishes, Oryō passed her inheritance to Mion rather than Akane. Since the Sonozaki family is quite rich, Mion has a large allowance. The 50,000 yen announced as the winning prize at a game tournament is said to come from her own pocket. She is a tomboy, and since she is the oldest among the rest of the students, she refers to herself as "oji-san (叔父さん)" – "old man (literally "uncle" but used generically)" – throughout the games, manga, and anime, though she also has a girly side. It is very often strongly hinted and ultimately revealed that she has a crush on Maebara Keiichi, which she expresses by picking on and teasing him at every possible occasion as well as confessing her feelings to her twin sister.
Due to being the oldest child and thus the heir, Mion was branded with the oni (鬼) – "ogre" or "demon" – tattoo presumably on her back. Her name also contains mi (魅), a kind of forest demon or elf.
Mion is actually the younger twin, and she was therefore born with the name Shion. Mion and Shion intentionally switched places when they were young because "Shion," the current Mion, felt it was unfair for only one of them to attend family meetings while the other had fun. They switched places the day the oni tattoo was to be applied, resulting in the younger sister, "Shion," the current Mion, becoming the next heir. No one but the twins themselves seemed to be aware of this. In the manga, when in danger, Shion asks Mion to allow her to be the "big sister." The switch is further developed in the manga in that Shion, rather than feeling cheated, expresses regret that Mion bears all of the responsibility she avoided.