How does a Hidden Mist ninja have the Byakugan?

Question

We know that the Byakugan is the dōjutsu kekkei genkai of the Hyūga clan of the Hidden Leaf. And each village does its best to try and keep such coveted powers to themselves.

But in a recent filler episode of Shippuden, Episode 358 to be exact, a ninja from the Hidden Mist was shown to have used the Byakugan and could locate Uchicha Shisui, thereby asking his team to retreat. How does a ninja from a village other than the Hidden Leaf and not of the Hyūga bloodline have the Byakugan?

Is this for real or is it just another mistake by the animators? Is there a mention of such a ninja in the manga(I follow only the anime and not the manga)?

Answer 1

Yes, there is a mention of such a ninja in the manga as well as in the earlier episodes of the anime.

The ninja that you are referring to is Ao.

He has clashed several times with Konoha shinobi. At one point he defeated an unknown Hyūga, taking one of the Hyūga's Byakugan and implanting it into his own right eye socket. Later, he had a confrontation with Shisui Uchiha, which left enough of an impact on Ao for him to clearly remember Shisui's abilities and his chakra colour long after the event.

He first appeared in the manga chapter 454 and Naruto Shippuden anime episode 199 (the five kage summit arc)