Sarikai is said to be over 700 years old thanks to the Genji. A woman never tells her true age but when she was younger she met a demon that would change her life. That demon was Bishamon, the son of a demon highlord. At her request, Bishamon gave Sarikai the power of the Genji. Even though it's an unstable demonic power, Sarikai passed that power on to those who enroll in The Academy, a military school of demon slayers she originated.

Bishamon

    The most hated demon in his world. Credited for introducing humans to the power of the Genji. A power used to fight against demons. Because of the curse bestowed upon him by his father for his betrayal, Bishamon died after rescuing Sarikai from a legendary demon.