Kyuu/History

Background
Kyuu's parents were in need of money, so they sold her to the livestock market when she was born.

Kyuu and San were both childhood friends of Louis while sharing the same cell during their time as raised livestock. After Louis was adopted by Ogma, Kyuu and San have since found ways to survive the Black Market together, and have presumably been companions ever since.

Revenge of the Love Failure arc
Kyuu is first seen in the present day when Louis and Legoshi accidentally fall through the ceiling after the building's elevator breaks. Louis is notably shocked to see both of his friends are still alive and well. Legoshi, not wanting to be rude, introduces himself to Kyuu, who silently takes out her knives from her ears and attacks him. San restrains Louis and tells Kyuu to attack Legoshi's left flank and right eyelid. Kyuu does so with astonishing speed, slashing Legoshi across the side, and commenting him as 'a buffet of old scars'. Legoshi manages to disarm her of her weapons but quickly finds himself being strangled by her rope. Once restrained, Kyuu prepares to cut out Legoshi's right eye, using his claw scars as tracing lines, but Legoshi manages to make her pause by pulling down her pants. While this makes her pause, Kyuu refuses to let such an act phase her, even telling Legoshi that he can look if he wants to, since he won't be using his eyes to see much longer. She questions why Legoshi didn't just kick her, and assumes that it was because he sees her as a female herbivore, a carnivore's supposed depiction of weakness; for this, she labels him as a dull male. She then looks to Louis and tells them both that she'll be selling their parts on the Black Market, but finally ceases her attack when she recognizes Louis as Number 4.

With the fight over, Legoshi is given stitches, and he and Louis express frustration on them attacking them outright. Kyuu and San introduce themselves, and Kyuu states her sadness at seeing Louis' foot gone. San explains their current lifestyle, where Kyuu fights in the Black Market's show arena and is said to be "crazy strong". Kyuu goes as far as to state that Legoshi's (mispronounced 'Degosi's') moves weren't bad, but was almost killed thanks to his "rotten nature". She reveals that she saw how he missed on purpose and declares it a weakness.