Okoi (Japanese: お胡夷, hiragana: おこい, rōmaji: Okoi) is a character featured in Basilisk: The Kouga Ninja Scrolls. Along with her older brother, Kisaragi Saemon, Okoi was chosen to be one of ten ninja to represent her clan of Koga Manjidani against the chosen ten of the rival Iga Tsubagakure clan.

Tomboyish and energetic with a well endowed frame, Okoi (in a manner similar to Rurouni Kenshin's Makimachi Misao, Naruto's Sakura Haruno and Soul Calibur's Taki) represents the popular concept of the kunoichi while Akeginu and Kagerou both embody the more historically traditional version. She has a close relationship with her older brother Kisaragi Saemon and is one of the few people who can make him smile. In the anime, she also has a close friendship with the normally unaproachable Kasumi Gyoubu whom she often goes with to hunt wild boar in the forests surrounding Manjidani.

Although 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 fasten her skin to theirs and drain 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.

In the Japanese original anime, she is voiced by Haruka Kimura, and by Monica Rial in the English dub.

Okoi VS Hattori Kyohachiro (episode 5): This battle takes place only in the anime. Sent by her older brother to check on Gennosuke at Tsubagakure (as Saemon believed Gennosuke would be less likely to get mad at Okoi for interrupting his time with Oboro than he would with himself or Gyoubu) Okoi was absent from Manjidani during the Iga's surprise attack when she spotted a suspicious ninja spying on her village from a treetop. When she demanded he identify himself, the ninja retreated with Okoi in hot pursuit through the branches and then along the ground. Okoi was just about to apprehend him when the ninja tricked her into falling off the edge of a sudden cliff. Okoi managed to save herself by throwing a weighted chain around a rock projection but lost sight of her quarry. The suspicious ninja was actually Hattori Kyohachiro; the adopted son of Hattori Hanzo the 4th who had been charged with observing the duel between Koga and Iga.

Okoi VS Nenki (round 1) (episode 6): On her way to Tsubagakure, Okoi stopped to get a drink from a river when she found herself surrounded by five Iga ninja: Tenzen, Hotarubi, Nenki, Koshirou, and Rousai. Seeing a chance to salvage some measure of victory from their failed attack on Manjidani, Tenzen attempted to trick Okoi into accompanying them to Tsubagakure. Okoi, however, saw through his deception and vanished into the trees. Believing herself safe, Okoi turned around and was shocked to see Nenki chasing after her, swinging from branch to branch by his hair. Okoi threw a trio of kunai at him and appeared to hit him before Nenki's staff came flying through the air and struck her in her stomach. With the wind knocked out of her, Okoi fell unconscious to the ground and was taken captive by the Iga.

Okoi VS Rousai (episode 7): After being captured by the Iga, Okoi was stripped and left tied up in the clan's salt shed where she found herself in the company of Azuki Rousai who demanded to know the techniques used by the remaining Koga ten. When she refused to cooperate Rousai smashed open a nearby salt bale and threatened to slice off her arms, her legs, and then her breasts unless she answered him. Okoi played the part of the helpless victim and enticed Rousai into caressing her exposed shoulder, whereupon Okoi successfully fixed his skin to hers as she began to drain his blood. Rousai struggled and Okoi managed to establish other points of contact, immobilizing him before attaching her lips to his throat and successfully draining the blood from his body.

Okoi VS Jingoro (episodes 7–8): Following her victory over Rousai, Okoi vomited out the excess blood and took the scroll he carried when she heard someone approaching the shed from outside. Okoi hid both the scroll and Rousai's body amidst the salt bales and assummed a helpless position on the floor just as Amayo Jingoro entered the shed to check on Rousai's progress. Okoi begged him to put her out of her misery, stating that no woman of Koga could live after being humiliated by an Iga as Rousai did to her. As she hoped, Jingoro saw the situation as a chance for personal gratification and began to strip. Once he positioned himself on top of her, Okoi attached herself to his skin and rolled over, pinning Jingoro to the floor so she could more easily drain his blood. Unable to break free, Jingoro dragged the two of them across the floor to the salt Rousai had spilled before Okoi killed him and rolled onto it to transform into his fluid state. Without any solid skin to hold on to, Okoi lost her grip and backed away in horrified revulsion at what Jingoro had become as he retreated into the safety of the salt bundles.

Okoi VS Nenki (round 2) (episode 8): After failing to kill Jingoro, Okoi snatched up the dagger he dropped and attempted to escape when Nenki arrived to see what was taking Rousai and Jingoro so long with the prisoner. Okoi slashed at him with her dagger and successfully broke Nenki's staff as well as the belt holding his kimono closed. Nenki quickly recovered though and managed to outmaneuver Okoi as she charged for a second attack, seizing her from behind by wrapping one arm around her neck and grabbing one of her breasts with his other hand. Again, Okoi attempted to drain the blood out of Nenki's body. But when she attempted to increase skin to skin contact, she found that the coarse hair covering his body protected him from her technique. At that moment, Okoi was fatally wounded as Nenki stiffened his hair into needles and impaled her across her entire body. As she lay dying, Saemon appeared in the form of Yashamaru and Okoi used her last moments of life to tell him all she knew before she finally expired, her brother silently comforting her until the end.

Okoi VS Jousuke (episode 16): This scene occurred during the flashback of episode 16. While hunting a boar with Gyoubu, Okoi took position within a bush while Gyoubu merged with the ground and prepared the seize the animal from below when something grabbed her rear; startling her into screaming which warned the boar into stomping down on Gyoubu's nose as it fled. The culprit turned out to be Udono Jousuke and Okoi and Gyoubu both chased him down the mountain before catching him at the spring where Saemon and Kazamachi Shogen were trying to fish. When Gyoubu suggested that they cook Jousuke for dinner instead of the boar, Jousuke unwisely joked that if Okoi ate something as fatty as himself than her hips would become too big; at which point Okoi soundly thrashed him.

In the manga, Okoi's personality stayed quite the same but her relationship with the other members of her clan is not expanded beyond Saemon; leaving most of her character to be underdeveloped in comparison to the other Koga.