Spirit

Spirits (精霊) are an entity that lives in the Spirit Realm.

Overview
Spirits can have children with mortals, but giving life to a child drains them fatally.

Half-spirits have incredibly long lives to the point one like Shirahime is still young after 2000 years.

Spirits never truly die, but their "lifetimes" can take different forms and genders; for example a brawny humanoid male spirit could come back as a female tiger.

Trivia

 * The six pillar spirits of fire, water, earth, wind, light and darkness are currently female.