ロゼ, Keroberos #3

She is one of Cerberus head and was the cause of giving Chiaki the curse. That was because she was frighten at the time.

she seem to be the healer of the tree heads but other than that its unknown

she was sent to Chiaki to be his guard dog by Chiaki's Father.

She also wear a mussel maybe do to the curse he gave Chikai

She appears when you pull Cerberus tail