I am working on updated biography for Yahru. I don't know where it will lead me but here it goes.
Yahru is a black, blue and silver Matoran who doesn't seem to belong to any sort of element. He showed up on Metru Nui at 250 BGC, when he landed on the shores of Ga-Metru. It was there that Yahru was found, taken in, and cared for by Toa Seihu. On Metru Nui, Yahru had a mysterious knack for inventing and testing vehicles, tools, and weapons, while developing an interest in the fighting style of his new mentor, Seihu. Where did this Matoran and his creativity come from? Where will this lead him and others around him? How will he find his role among his fellow Matoran?
Yahru has a mysterious personality. On the one hand, he can be calm, creative, flexible, practical, and rational. Other times, he can be spontaneous and difficult to read. He also doesn't like to be tied down in only one way of doing things, even if it's for a worthy cause. Sometimes his risk-taking can get him and others in trouble, which is something he'll need to work on if he's going to be a part of a team.
That's as much as I can give right now. Let me know your thoughts in the comments below.