Tsunokakushi

Haruka, an orphan, is granted special permission to transfer to Abelia Academy, a school only for chosen ladies. Just as she is met with piercing stares, she encounters Sayo, a classmate with an alluring aura, and her brother. Haruka's fate is sealed as she becomes entangled in the secrets that plague the academy... A love triangle woven by humans and demons.

(Source: Shounen Gahousha, translated)