Mecha Sion theory

It's a pretty wild guess, but I believe that Mecha Sion was hacked by Creator .

Based on the text that teased the skin, we can definitely assume that Mecha Zero Sion was a malfunctioning prototype that was activated by someone who breached the system that protected it. Considering the fact that Viktor is probably the only evil genius in Runeterra with the knowledge to do such a thing and that mechas are created in a distant future by (a Piltovian), it's easy to understand the motivations behind the actions of our beloved Zaunite trans-human.

On top of that, Mecha Sion shares some lines of dialogue with Viktor, one of them being "Function over form", that heavily hint at a connection between the two that is more than just sharing the same point of view.

The sad thing is, always ends up losing his free will and becomes a slave, both in the main universe and in the futuristic setting of Battlecast vs Mecha.