TL;DR: the Toa Team prior to the main series fights the Kanohi Dragon (or dragons) as they are sealing the Kanohi Masks away.
In the First Toa Team pitch by @JediTimeLord824, he wrote about his picks for the First Toa and their role in the lore, but after some discussion it seemed better to have this team be the ones to confiscate the Kanohi Masks. This would involve a betrayal from one of the Toa and the last survivor banishing himself into the wilderness.
In the City of Masks pitch I wrote 4 days ago, I introduced where the Kanohi Masks were made and how the Toa ultimately rendered the mask-making process there unusable.
In a Mahri Nui pitch by @AntrozT6, I read about how the Barraki could have once ruled the island, which helped me with an idea for the Barraki to hoard the Kanohi Masks for themselves and abuse them to their own ends. This would cause the Elemental Gods to send the Toa to defeat the Barraki and dispose of the masks.
In this pitch, combining the three mentioned pitched above, the Barraki take the Kanohi Masks for themselves, weaponizing them to the nth degree in every conceivable way. They use this power to oppress the people and terminate rebels.
One of their weapons is the Kanohi Dragon(s), a large, lizard-like Rahi adorned with Kanohi Scale Armor. The Kanohi Dragon would act as the ultimate enforcer on the island, obeying the Barraki as it quells any outcries.
Due to its threat to the island (overwhelming power and ferocity), the Elemental Gods summon the Toa as a last resort to overthrow the Barraki. Allying with various rogue villages, the Toa are able to kill the Kanohi Dragon and seal away the Kanohi Scale Armor, breaking it up into multiple masks before hiding them from everyone else.
However, during the revolution against the Barraki, one of the Toa (explained in @JediTimeLord824’s topic) betrays them, although specifics are still murky. To keep the summary short, only one Toa survives (explained in the same post mentioned).
Well, that about sums it up!