Fū Yamanaka

(Foo in the English manga) is a ninja of Konohagakure, a member of the Yamanaka clan and a seemingly high-ranking member of the Foundation.

Five Kage Summit arc
Fū is hand-picked by Danzō, along with Torune, as one of his unmasked escorts, to protect him during his journey to the Kage Summit in the Land of Iron. Before departing, Fū asked Danzō about how they should prepare for the trip; Danzō told him to not worry about it and prepare in any way he sees fit.

Later, he is seen walking with Danzō and Torune, and the group is attacked by the Hanya Assassins from the Land of Wood. Danzō tells them not to do anything and brutally defeats all the assailants. When the Raikage became too violent, he and Torune, along with the other kage escorts, jumped into a defensive stance. He was told by Danzō to stand down. When White Zetsu appears during the summit, Fu and Torune guard Danzō. When him and Torune try to go and battle Sasuke they are stopped by Ao who was told to watch them by Raikage. Fu and Torune try to attack but are stopped by Danzō. He later reveals to Danzō that their location has been found out by a member of Sasuke's squad, and he asks what they should do, to which Danzō replies that they stay where they are, and if attacked, they could use the confusion to escape. When Sasuke and Karin get to where the summit is taking place, Fū, along with Torune and Danzō, escape but they are chased after by Ao.

Realizing this, Fū sets several traps in preparation for his special jutsu. Before activating it, Danzō orders Fū to make sure to not damage Ao's Byakugan. Fū then proceeds to transfer his mind to his puppets and begin his assault on Ao. After luring Ao close enough, Fū takes control of Ao himself. Unfortunately, he is unable to remove the Byakugan eye because of a special seal protecting it. Fū improvises by instead deciding to decapitate Ao. Fortunately, the Mizukage arrives in time to save Ao. Hoping to trick the Mizukage to remove the seal, Fū pretends to be Ao. The Mizukage is able to see through the lie and beats up Ao's body to free him, unaware that Fū already ended the jutsu.

Nearing Konoha, Fū, Torune, and Danzō were ambushed by Madara Uchiha. Danzō told Fū and Torune to cover him, as he prepared to release his right arm, which belonged to Shisui Uchiha, along with his right eye. Before engaging Madara, Fu told Torune that they have to watch each other's backs. They than charge into battle. While Torune distracts Madara by throwing kunai, Fu sneaks up from behind and tries to change into Madara's body. However, before the jutsu activates, Madara uses his teleportation to go through the pillar they're fighting on. Just when Fu states that Madara's chakra has vanished, the Uchiha comes back through the pillar just behind the former. Fu slashes at Madara with his sword, but it passes through the latter harmlessly. Madara solidifies himself once again and grabs Fu's blade, readying himself to attack. Before he can do so, Torune throws another kunai, which although shattering upon impact with Madara's mask, the distraction works well enough to save Fu. Madara then identifies Fu as a member of the Yamanaka clan.

Fu and Torune strategize and Fu chooses to be the decoy while Torune prepares his attack. Fu comes at Madara with his sword, but it harmlessly passes through once again and Madara attempts to strike Fu. Torune chooses this oppertunity to attack the Uchiha, but Madara's attack was just a decoy as he easily sees through the deception and Torune passes through him, striking and poisoning Fu instead. Cursing themselves for falling for the trap, the poison in Fu's arm is than healed by Torune. After being cured, Fu apologizes to his partner. Torune brushes him off and tells the former to keep an eye on Madara. Before Torune can use the poison, Madara sucks him into another dimension, shocking Fu. However, by doing so, Torune infects Madara's right arm, making the Uchiha sever the arm and kick it towards Fu, who barely dodges. The distraction works long enough for Madara to pull Fu in as well.

Abilities
Danzō stated that he and Torune are two of the most-skilled ninja in Root. Fū also appears to be a sensor. He is skilled enough to detect Sasuke and Karin planned to approach them, and that Karin is a sensor type. His reflexes are fast enough that when Madara Uchiha reappeared he instantly sensed him and counterattacked.

Fū is also an expert in trap making. He regularly uses this skill with a cursed seal variant of the Yamanaka clan's Mind Body Switch Technique, which he transferred his consciousness into a strange scarecrow like body with kama for limbs and proceeded to attack Ao. Although seemingly easily defeated, Ao then found that a secondary skill similar to the Cursed Mark switched his perception with the scarecrow. All the while, Fū was unconscious and being carried around by Torune, much like the Yamanaka technique.

Trivia

 * Lake Yamanaka is a Japanese lake that is located at the base of Mount Fuji, which means this might be where they got Fū's name from.