Seraphim

Seraphim, usually called Sera, is a vampire ninja who combines the Tsubamegaeshi sword technique and ninja reflexes with supernatural abilities. She can form bat wings and a katana from leaves and periodically needs blood to survive. Sera comes to Ayumu's home hoping to serve Eucliwood, but after being rejected she becomes Ayumu's servant instead, treating him coldly while respecting his fighting ability.