Shion Ogura is a 15-year-old student at Sakuragaoka High School and a member of the Black Magic Research Club, residing in the attic above the Yoshida household alongside Momo and Mikan Yoshida. She is friends and classmates with Yuko Yoshida and Anri Sata. Standing 154 cm (5'1") tall, she has long black hair usually tied with a black hairband, blue eyes, and wears circular glasses. Her birthday is December 14 (Sagittarius), and her blood type is A, though sometimes mistaken for type B.

A genius with a mad scientist-like dedication, Shion throws herself enthusiastically into researching black magic. She collects extensive occult information and excels at deduction and fast reading, yet possesses a notable lack of ethical knowledge, leading to unconventional or morally ambiguous methods. She harbors a specific fascination for her friend Yuko, admiring her heritage as the Dark Clan heiress. Shion openly praises Yuko's demonic traits like horns and tail, remarking, "They're so stylish. Totally fitting for a Demon Girl" and "Don't try and hide them, they really suit you!"

Her name originates from the demon Gusion (Ogura Sion), associated with knowledge, time, and tomes – a connection she once acknowledged by signing a plan as "Gu-sion." Gusion describes her as "a fragment of myself I left behind, the last page of my life's story." Despite this lineage, Shion exhibits no supernatural abilities beyond her accelerated reading and strong deduction. She primarily supports Yuko's endeavors using her occult expertise or club resources. Shion openly envies those with grand destinies, stating, "I'm totally jealous. Having a destiny is so cool."