Whetu and Onupi are two very different, yet very similar Matoran.
Whetu is a miner, a grunt worker toiling in the vast mines of Onu-Wahi, digging for Lightstones, protodermis and other valuable minerals. He's down-to-earth with the heart and mind of a worker, much like the countless other miners he works with.
Onupi, on the other hand, has more in common in terms of personality with Ko-Matoran than his Onu-Matoran comrades. Not much of a speaker, Onupi is Onu-Koro's most skilled surveyor, and his name is known across Mata Nui for never making a mistake and always finding the best veins. Not he, nor the other Matoran, and not even Turaga Whenua know that this isn't talent, but rather a glitch that allows him to minimally utilize his Kanohi Akaku, a feat no other Matoran is capable of.
Despite being so different, Whetu and Onupi are bound by a friendship unlike any on the island of Mata Nui. For outsiders, it might often seem like they hate each other, as constant insults aimed at their different positions fly between them, but it's all in good fun and their way of communicating. They would be willing to die for one another, their friendship more like brotherhood.
This theme of "similar yet different" continues in their builds. They have similar body shapes and sizes, however Whetu's torso is Slizer-based, Onupi's is fully custom using small Technic doodads.
Whetu's drill has a working gear function, and his security frame still allows minimal head motion, and he can actually see out of it too. Onupi, when carrying his tablet "wears" his thumb on his back, concealed by the cape.
Flickr album: https://flic.kr/s/aHsmbUEzt6
As always, comments and criticisms much appreciated!