San (Alpaca)/History

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

Revenge of the Love Failure arc
San 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. When Kyuu looked at Louis's eyes, she recognized him as Number 4 and ceased the attack.

With the fight over, Legoshi is given stitches, and he and Louis express frustration on them attacking them outright. San explains their current lifestyle, where Kyuu fights in the Black Market's show arena and says she is "crazy strong".