In the original Bionicle canon, kaita could be created by any three beings of the same species, who would willingly forsake their individuality and merge their forms into a bigger, more powerful being with its own personality.
Here in Corpus Rahkshi, things work a little differently:
"Kaita are also possible, though there are a few restrictions on forming them. First, they can only be formed by characters from three players, no roping in a couple of NPCs to make yourself suddenly bigger and stronger. And each specific combination requires a profile be filled out and approved beforehand of what the Kaita would look like and what additional power it gets upon formation. Finally, in a slight change from how Rahkshi Kaita usually work, the minds of all three participants are present and have the potential to control the one body, but they have to be working together to maintain the fusion. You can't simply have one player performing one action while another makes an entirely different and separate attack and the third trying to retreat because that loss of unity will result in the Kaita simply dissolving back into three Rahkshi. You need to all be working together to the one goal, co-ordinating your efforts as a team for the Kaita to actually work."