コハク

The pretentious speech doesn't match the youthful looks.

 A person of many mysteries who has a dignified presence.

 The sword at the waist is 2 shaku 7 sun long (~81 cm).

 The left eye is constantly closed.

 Age and gender are unknown.
Solelo website

It confirms later that Kohaku is female and couple of hundred years old. She had a twin-brother in past.

She is the foster daughter of Rouryuu./