Ksai is a boy known to be famous for computer technology. However he is also one of San Rokata's bullies at the orphanage. Ksai bumped into a crawling Ksai, who was crying to have playtime (which involves him hitting his diaper, filled with poop and unchanged for years, on someone and repeatedly saying poopy). When San spotted Ksai, he immediately crawled toward his direction crying wanting to play when suddenly Ksai brought up how giant his butt is. A mirror was next to a confused San and he turned to see his butt ginormous and bubbly as well as seeing rashes on it. He turned around to look at it and was shocked to see it. Turns out his butt was accidently injected with puss at a lab facility. That was the same time he got extremely mocked at for making an accident in front of the other orphaned kids. All the kids gathered around him calling him "Poopy", hence where he got the word. While Ksai wasn't responsible for making the crowd, he was still part of it. The trauma that San experienced made him suppress all his childhood memories, hence why he only thought about playing by hitting his years of unchanged diaper filled with poop using his butt. It was also the reason why Brick screamed in pain when San did that. Ksai is known to be very narcissistic and known to be a mocker. Unfortunately for him, that turned on him as he now witnessed San's expression changed from happy all the way to autism rage. San began to use his giant butt to repeatedly crush Ksai, who is now helplessly on the ground, and repeatedly screaming poopy due to anger. Ksai was in tears begging for mercy, but all of San's life was nothing but playtime before then as all the childhood memories were suppressed. Ksai then heard a tightening grunt, as if San is pushing something. Ksai immediately knew what was going to happen. Butt faced towards Ksai means San is about to drop a giant load on him. Just when it was about to exit, Chi smacked San using the side of his sword, sending San flying to the wall. When Chi took Ksai to the hospital, he asked why he would join in the crowd despite knowing there will be consequences. Ksai told him that he just wanted to fit in, afraid he might be judged by others for standing up for a severely autistic boy. Ksai saw the error in his ways and decided to quit school, since going there will only make him feel worse. He dropped out and began his own working place for computer technology. He also had to get stitched too, since the impact crushed his front skull. His true personality was then finally revealed: a lazy guy known to be a bit of a glutton and let's out many gasses from his body. Ksai is also more kind and considerate and apologized to San a year later after everything cooled off.