So this theory came about when I was wondering how a sixth of a toa's power could become a full supply of toa power. I came up with this. Inside of matoran destined to be toa, there is a small chamber with a full supply of toa power. This chamber is made of a substance harder than protosteel, and can only be broken by toa power channeled through a suva, kanohi, or other channeling device.This explains why helryx was able to allow krakua to fulfull his destiny early, but not just some random matoran loyal to the order. Only matoran destined by the great being would have these chambers.I also propose that these chambers also contain mutigins of the same type the makuta use. These mutigins would transform the matoran into a toa.This is not as far-fetched as you might think. The great beings often reused stuff, including built in rohtuka spinners, and kanohi. The toa power is seperate from the size increase, as in the melding universe, the toa were the size of matoran, but had full toa power.The mutagins also tie into the last part of my theory. When a toa sacrifices their toa power, I think that their body then cleans out the virus's which causes the toa to revert to a matoran like state. But virus residue results in the turaga to be a little bigger than a matoran, and their minds are still mostly as it was as a toa, allowing use of noble masks.This makes sence because essecially, the only real difference other than mask use between a matoran and turaga, is the wisdom accumulated from time as a toa. The only time we see turaga as being significantly bigger than matoran was in 2001, and those matoran had been shrunken by the matoran spheres.Summery:My theory is that matoran destined to become toa have a small chamber inside them, harder than protosteel, that can only be broken with toa energy. The power in the toa stone is channeled through the shrine or mask, and breaks open this chamber. It contains a full amount of toa energy, and mutagenic viruses (like the makuta use) that change the shape of the matoran to a toa. When a toa becomes a turaga, they loose all their toa energy and virus, reverting them to a matoran like state (seriously, they are the same size as matoran), but the power residue and mental capacitys stay, allowing useage of noble masks.