The Ultimate Vampire Resource and Directory

Okoi
Voiced by: Haruka Kimura (Japanese), Monica Rial (English)
Tomboyish and energetic with a well-endowed frame, Okoi embodies the popular concept of the Kunoichi (in contrast to both Akeginu and Kagerou who embody the more historically traditional version). She shares a deep bond with her older brother Saemon and is one of the few people who can make him smile. In the anime, Okoi also has a strong friendship with the normally unapproachable Gyoubu whom she often goes with to hunt wild boar in the forests surrounding Manjidani. Although she's a capable fighter, Okoi is not opposed to using her ample assets to lure men into a state of false security if she has to. For once they make the mistake of forming physical contact, Okoi is able to adhere her skin onto her opponent's and then absorb their blood into herself; leaving her enemies as dried up husks. Upon completion, Okoi must then vomit out the excess blood before she can use the technique again. As more contact equals faster blood drain she is dressed in a more revealing manner than the other kunoichi with a hip length sleeveless kimono and shortened hakama that resemble Daisy Dukes.

I copied the information from Wikipedia but I have also watched the series. Okoi is a strong female character. She has a very strong sense of family and high intelligence.
The method in which she saps her opponents energy and life through their blood was a beautiful and sensual imagery.