A character from TYPE-MOON's Tsukihime and Melty Blood series, first appearing in Kagetsu Tooya. Len (or Ren) is a succubus by nature, and can turn into a cat, which is fine, too.
Portrayed as a girl with long, blue hair; red empty eyes and pointy ears. She tends to be mute, rarely ever speaking in her humanoid form.
She serves Tohno Shiki as a familiar.