Board Thread:Wiki Discussions/@comment-24925932-20140510165758/@comment-1705651-20140510204545

As of now I think Hagoromo's brother only exists to explain stuff like the Byakugan, which weren't a part of Hagoromo and his sons' powers, and other minor inheritages like Kinkaku and Ginkaku.

As of now he was only mentioned once and wasn't that important in the overall mythos of the series, making it nearly impossible to theorize about him.