Yūkimaru

is a young boy (it is still unknown if he is a shinobi) who appears in the second Naruto Shippūden filler arc. He seems to be another test subject of Orochimaru.

Hunt for the Three-Tails Arc
So far we have only seen him once in this arc, collecting tree flowers after Sasuke Uchiha cut them off with his Chidori for his training.

Trivia

 * Based off appearance, Yūkimaru looks very similar to the Three-Tailed Beast's former Jinchūriki, who was revealed in splash page of chapter 420.
 * On a side note towards Yukimaru possibly being the Three-Tailed Host, in the picture featuring all nine hosts, you can clearly see the Three-Tails host with a giant hook behind her (possibly weapon of choice) which has a flower on it. This can be a reference to when the first time we see Yukimaru, he's picking up flowers and he seems to know about the particular one he picked up.