Yūkimaru

is a young boy (it is still unknown if he is a shinobi) who appears in the second Naruto Shippūden filler arc. He is a test subject of Orochimaru, because he has the ability to control the Sanbi.

Personality
Yuukimaru is a quiet boy, probably due to his past, he constantly ask's questions like "Is it going to be fun". His main goal is to find home and is told by Naruto that home is a place where people think about you, which lightens his spirit.

Hunt for the Three-Tails Arc
When Sasuke Uchiha trains, he cuts off tree flowers with his Chidori. After that we can see Yūkimaru collecting the flowers. Sasuke tells Yūkimaru to go home and he replies he has no home to go to. Later on Kabuto sets off together with Yūkimaru for a journey. They eventually arrive at a dark swamp. There, Kabuto conducts an experiment where he forcibly releases the full power of Yūkimaru's chakra. This results made the Three-Tailed demon to partial emerge before submerging again. Afterwards, Yūkimaru is left exhausted, but Kabuto finds the results satisfactory. Later on the way back to Orochimaru's lair, Kabuto lets Yūkimaru take a rest at a hot springs, that Naruto is coincidentally at as well. There, Yūkimaru meets Naruto and they talk about bonds, making Yūkimaru glad that there may truly be a place for him. He then leaves a clueless Naruto to wonder who he was.

Later, he is sent out again with Guren to complete a mission. During which, he succumbs to sickness, forcing Guren to care for him. As a result, he seems to have grown attached to Guren and possibly vice-versa. This is further emphasized from how Yūkimaru reacted when Guren tells Yūkimaru she has to head out in a manner similar to how Yūkimaru's mother did before presumeably dying. He then gives her his necklaces with a special charm on it.

Later, Yukimaru again bumps into Naruto, who offers for the orphan to join him in Konoha, to which Yukimaru politely declines as he feels his place is with Guren. Soon after, Kabuto returns to conduct another experiment with Yukimaru. He has Yukimaru take several medical pills. Ultimately, this finally causes the Three-Tailed Beast to emerge.