Setsuna

Setsuna is a half-demon demon slayer who works under Kohaku. She was separated from her older twin sister Towa when they were both four-years-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 wields the weapon Kanemitsu no Tomoe.

(Source: Inuyasha Wiki)