Yuukimaru is a new character added in Naruto Shippuuden Episode 90. I can't seem to find this character in Naruto Manga Volumes. If i'm not mistaken, Yuukimaru character really is not a part of the Naruto Manga Volumes.
Yuukimaru:
In Naruto Shippuuden Episode 90, Yuukimaru had a scene with Sasuke and Kabuto. Yuukimaru calls Sasuke as Sasuke-san. Yuukimaru seems to be a nice, kind and innocent character. He doesn't know much about things and the surroundings always amazes him, like it is his first time to see those things. Yuukimaru's skills is not exposed yet but it is clear that Yuukimaru is one of Orochimaru's specimens.
In Naruto Shippuuden Episode 92, Kabuto drew out Yuukimaru's energy through a medicine and a helmet-thing on Yuukimaru's head. A creature underneath a lake appeared partly when Yuukimaru's energy was drawn out. Yuukimaru's energy appears to have awaken the creature. The creature on the lake is the 3-tailed beast or Sanbi.
On one hand, after that lake event, Yuukimaru meets Naruto in hotbath. They had a small conversation [about "home"] but Naruto wasn't able to know his name.
