Kaita were fusions of three beings into one single being.
Toa Kaita were a fusion of three Toa. Once the beings fused, they merged into a completely different being with a distinct personality, Kanohi, and weapons. Only two Toa Kaita have been seen thus far: Akamai and Wairuha, formed from the Toa Mata. Other Toa could form Kaita, but didn't. Toa Hordika couldn't form Kaita, as they lacked the mental focus to stay together.
Matoran Kaita were formed when three Matoran fuse. As long as they have separate Elements, they could be formed.
None have appeared in the storyline, but two could be created from the McDonald's sets.
The Rahkshi Kaita were fusions of three different Rahkshi. Only two have appeared so far:
A Bohrok Kaita was a combination of three Bohrok into one. Unlike most Bohrok, these had two Krana. None have appeared, but two are known to exist:
The Bohrok-Va Kaita were fusions of three Bohrok-Va into one larger being. None have appeared in the story, but two were combiner sets.
Three of the Bohrok-Kal could also merge to form a Bohrok-Kal Kaita. Only one has appeared in storyline, though two are known to exist:
|Matoran: Toa Kaita (Akamai • Wairuha) • Matoran Kaita • Turaga Kaita
|Matoran: Matoran Nui • Turaga Nui|
|Skakdi: Piraka Fusion • Golden-Skinned Being|
|Dark Hunters: "Prototype"|