Eiko Oni is a freshman student attending Babylus Demon School. She constantly tries to have a conversation with Iruma Suzuki ever since he saved her but fails every single effort throughout the series.
Eiko is a female student wearing the typical female student uniform with no discernible changes. This includes the typical blouse and a pink capulet, with a pink skirt and red bow with a cat-eye clasp at her neck.
She has long, somewhat frizzy blonde hair which is not tied back. She has uneven bangs framing her face. She has two black, bull-like horns on either side of her head, and pointed demon ears. She has large, round, yellow eyes and short red-painted nails.
Eiko is a somewhat normal high schooler; she has very few outstanding qualities. She's somewhat sociable, as she's usually seen casually talking to multiple unnamed background characters, but mainly hanging with her close group of friends.
She is somewhat shy when talking to people she admires, such as when she attempts to thank Iruma for saving her, on multiple occasions. In this way, she appears polite and kind in nature.
Iruma Suzuki - She holds Iruma in high regard and is grateful for him saving her from harm during his duel with Asmodeus. Eiko has unrequited feelings for Iruma, as she occasionally tries to get close to him, but always fail in the end.