First off, the concept of a Toa Ahkmou, even tho is very commonly used, is always very interesting. However, Ahkmou joining the Order of Mata Nui and actually becoming a good guy seems out of character for him.
But onto the moc: The over all moc is a pretty simple build, but I guess it fulfils its job. I don’t like the colour scheme, tho. Too much light grey. I would change it with brown or black, but especially with brown, because you know… He is a Toa of Stone, and the Stone beings are brown, and this thing don’t have enough brown in it. There are also blue and red pieces that disturb the colour scheme.
The build of the torso seems good. The arms however are weird. They remind me of a Toa Hordika. But this should not be a Toa Hordika so… But one thing I don’t like at this moc is that it is pretty short. It’s legs are stubby, the torso is too short, and the arms are gigantic. They are just too long for the whole moc.
And now the backstory. As I said, the Toa Ahkmou concept is pretty neat, but I don’t really think it fits in this case. Why did he joined the Order of Mata Nui? Because Takanuva helped him to kill Teridax once and for all? And why did he joined the Order? Takanuva is not part of the order, mainly because there is a rule that no Toa can become a OoMN agent (well except for Helryx and Krakua). So unless this rule is deleted, and everybody suddenly trusts Ahkmou (which nobody would, knowing the bad things he have done), he can’t become an agent.
Over all, nice first attempt for the first version of the self-moc.