Yūkimaru

is a young orphan boy who appeared in the Naruto Shippūden anime. He was a test subject of Orochimaru, because he had the ability to partially control the Three-Tailed Giant Turtle.

Personality
Yūkimaru is a quiet and gentle boy, probably due to his past. He constantly asks questions such as "Is it going to be fun?", and "Am I going home? Do I have a home?" His main goal is to find home, and was told by Naruto that home is a place where people think about you, which lightened his spirit. In the end, he decided that his home is with Guren.

Three-Tails Arc
Kabuto conducted an experiment on Yūkimaru by forcibly releasing his chakra, partially calling forth the Three-Tails. Kabuto was satisfied with the results, and took an exhausted Yūkimaru to Yugakure to rest. There, Yūkimaru met Naruto Uzumaki, and they had a brief discussion about bonds. Soon afterwards, he was sent on a mission with Guren, but became sick along the way. Guren took care of him and they grew close, Guren reminding him of his mother. Guren gave him a crystalized camellia, telling him that it would never wither for as long as she was alive. Once he got better he ran into Naruto again, who offered to take Yūkimaru back to Konoha. Yūkimaru politely declined, as he felt his place was with Guren.

Later, Kabuto conducted another experiment with Yūkimaru; by consuming more pills than the first time, he was able to completely summon the Three-Tails. The strain caused his nose and ears to bleed, and he soon passed out, causing the beast to go on a rampage. When he woke up, he found Guren fighting the beast in order to protect him. Yūkimaru used his remaining strength to keep it away from her, but they were quickly washed away by the Three-Tails.

After recovering from the ordeal, Yūkimaru found Guren and Naruto arguing over him. Yūkimaru told Naruto that he was happy to have met him, because now he had a place to be: with Guren. When Guren engaged the Three-Tails again, Yūkimaru restrained it without the aid of Kabuto's pills for a short while. The beast escaped from his control, however, and Yūkimaru passed out. A group of Konoha ninja found and attended to him, and when he came to he told them that Guren and Naruto had been eaten by the Three-Tails. Yūkimaru helped them locate the beast and, after finding it, went to hide with Sai. He was quickly captured by Rinji.

Taking advantage of Yūkimaru's feelings for Guren, Rinji convinced Yūkimaru to take more of Kabuto's special pills and use his powers to control the Three-Tails. He used all of his strength to bring the Three-Tails to their location, and, as he collapsed, he was caught by Guren. Rinji went on to inform Yūkimaru of the fact that Guren had killed his mother, something Guren admitted to. Yūkimaru was speechless, but Naruto interjected, speaking on behalf of Guren by telling Yūkimaru how much she had changed; while the past Guren had committed terrible sins, this Guren was regretful of her past transgressions. Guren added that, if he would allow it, she would protect him forever. Yūkimaru accepted.

Rinji attacked them, in doing so revealing himself as Kabuto. Kabuto explained what Guren and Yūkimaru's purpose was: for the two of them to get close and become dear to one another, so, when Yūkimaru learned of Guren's murder of his mother, he would use his anger to make his power explode, although he was visibly surprised this hadn't occurred. He continued to speak about the violent future ahead for the entirety of the Ninja World, and that being their reason for using Yūkimaru to gain the Three Tails.

While Naruto fought with Kabuto, Guren and Yūkimaru fled. Kabuto sent Rinji's animated corpse after them, so Guren defended Yūkimaru. When her Crystal Release attacks proved futile against Rinji's bats, Guren encased herself and Rinji in crystal, and they fell into the lake. Believing Guren to be dead, Yūkimaru let loose his power, driving the Three-Tails into a frenzy, and shattering the seal the Konoha ninja were very close to completing. Once the beast was driven off, Naruto found Yūkimaru, and brought him back to the other Konoha ninja to rest. Whilst there they discovered that his body had not been able to handle the strain, and he had lost his ability to control the Three-Tails.

Yūkimaru awakened to find the crystal Guren had given him fully repaired and glowing. He rushed off into the night to find her. Naruto, after realizing he was gone, went to search for him - but when he found Guren's crystal left in a patch of bushes, unblemished, he knew where Yūkimaru had gone, and decided to leave him be. He put forth this point to the rest of the Konoha ninja the following morning, deterring them from searching for Yūkimaru. As the Konoha ninja were leaving, Yūkimaru, alongside Guren and Gozu, looked down upon them, and Naruto saw them walk away. Yūkimaru's hand was seen holding Guren's, as they walked into the distance.

Trivia

 * Because of his connection to the Three-Tails, Yūkimaru is believed to have some connection with its former jinchūriki, Yagura. They have similar appearances, and both have an apparent connection to flowers, however, Yūkimaru is an anime-only character that does not appear in the manga.
 * Yamato referred to Yūkimaru's mysterious usefulness to Orochimaru as "the ability to synergize with a Tailed Beast".
 * Yūkimaru's favorite flowers are white camellias.
 * In the omake in Naruto Shippūden episode 134, Yūkimaru made a cameo along with Guren on Commemorating the Ep. 350th

Quotes

 * "I like red camellias. I like white camellias. Camellias drop the entire flower, not just their petals. You can remove the oil from the flower, and the tree itself can be used to make ink."
 * (To Sasuke) Is this where I'm supposed to return to? But something's not right. This is not the place where I'm supposed to return to. That's right... you wouldn't know that would you? Say, do you have somewhere to go back to? 
 * (To Guren) You're a nice person, Guren... you are the one I should return to, after all... and I'm the one you should return to, Guren. 
 * (To Guren) Uh-huh... and I will always think of you, Guren. For now and forever... and ever... I love you. 
 * I wonder where my home is.