Board Thread:Theories and Speculation/@comment-1512913-20150221101637/@comment-1512913-20150222120237

The Hyuga themselves are descended from the Otsutsuki, Hamura to be exact, so mixing chakras of Hamura's human descendants with his non-human descendants simply restores Hamura's chakra thus the Tenseigan, but that doesn't explain how he had it in the first place. The Rinnegan and Sharingan seem like split Rinne Sharingan, but the Tenseigan seems superior to the Byakugan, so it's a mystery.