It began because Xigbar was a superior. He was of the original six. He had a name and memories. Conversely, Roxas was the lowliest. He not only didn't know his previous name, but he also had no memories and that made him garbage, at best.

But it began because the City was like a cage and the Castle was like Hell. There was nothing for them anywhere in the universe. They could go to Agrabah and eat as many plates of warak enab and drink as much yansoon as they wanted and it wouldn't mean anything. They would taste it, but their bodies didn't need the nourishment and their hearts gained no joy.

The thousands of well meant quotes decrying the merriment of food were nearly insults to the Nobodies who had no love sincere and no intimacy with which to act. At least, nothing outside of the realm of simplistic physicality; and therein lies the issue. It was maddening and it was frustrating.

It drove them to fight like the great caged beasts that they truly were. They were creatures helplessly struggling with the snares of their bodies, reaching for livelihood, infuriated and afraid. Indignant. Unsatisfied. The contortions and spasms of the emotionless soul.

No one in Organization XIII had sex and they definitely didn't 'make love' or any other disgustingly kind little euphemism. The Organization fucked and rutted. It was hurried, fast, painful, and bloody. It was rape without consent or consideration or consequence. The six were untouchable even though they could have any of the others they chose. Within the lower ranks, however, the field was open.

The Superior made it abundantly clear what Number XIII was. He was a tool to be used as seen fit.

And that was how it was allowed to begin.

Disclaimer: I do not own Kingdom Hearts