Setsuna

is a half-demon demon slayer who works under Kohaku. She was separated from her twin sister Towa when they were both 4-year-old, but was reunited with her after traveling to the future with her cousin Moroha. She seems to have difficulty believing Towa is really her sister. She has a calm, unflappable personality much like her father, Sesshōmaru. She also seems to have some sort of sleep-related childhood amnesia.

Trivia

 * While it is known that her father is Sesshōmaru, her mother's identity is so-far unknown.
 * Unlike most other hanyō, including her uncle Inuyasha, Setsuna does not have any visible, physical indicia of being a half-demon, such as dog ears.
 * Setsuna's name, like that of her sister Towa, is homophonous with a time word, "moment". This is likely an allusion to the fact that both sisters travel through time.