Motoi is a minor character in Naruto, first appearing in Naruto Shippūden, being a ninja of the Hidden Cloud stationed on the giant turtle Genbu to prevent Naruto from learning about the war breaking out. Motoi is Killer B's best friend, and learns to trust Naruto, who would go to fight upon inevitably learning about Obito Uchiha's war. He assists the two jinchūriki and other allies in any way he can even if it means taking risks, assisting to put an end to Kisame Hoshigaki and stopping the reanimated Fukai, the original Killer B forced to fight for evil against his will.
He is voiced by Yasuhiko Nemoto in Japanese and by Sam Riegel in English.
Motoi is an exceptional tracking ninja, who's chakra nature was Lightning. His skill with Lightning Style was enough for him to stand up against Fukai in his Eight Tails Chakra Cloak, and temporarily halt him. Though his skill in ninjutsu may be fine, he appears to lack skill in hand-to-hand combat, with only Kakashi and Guy being able to fight Kisame Hoshigaki.
As supervisor of the Island Turtle, he knows all about it, though only Killer B has tamed all of the creatures on the island due to his charisma and immense power. He shares a link with the barrier surrounding the Island Turtle, being able to pinpoint where an enemy is trying to get in from. However, this is not the ability of hyper-sensitivity, simply a link with the barrier, so he cannot sense the locations of people inside the island.
He has a summoning contract with owls, which he uses for long distance communication.
Motoi and Killer B have been friends since childhood, even before Killer B became a jinchūriki. Motoi's father died to the Eight Tails, after it was released from Blue B and had to be sealed immediately. Motoi harvested that same resentment towards Gyūki that Iruka Umino felt towards the Nine Tails when it killed his parents, and subconciously redirected that hatred towards Killer B once he became the newest jinchūriki of the Eight Tails.
One day, Motoi attempted to assassinate Killer B, an attempt which failed and left him in shame. His shame wasn't because he failed to avenge his father, but rather because B harbored no ill will towards Motoi. Killer B with Gyūki sealed inside him became legendary heroes of the Hidden Cloud, and Motoi had trouble interacting with B out of guilt of his actions.
Naruto Uzumaki was sent on a high-rank mission to an obscure island near the Village Hidden in the Clouds. After a long and arduous boat ride, Motoi greeted Naruto and his Konoha escorts. Seeing that his destiny was to be trained by an octopus, Naruto demanded that Killer B train him, though he refused. Naruto then goes to Motoi, who then tells him that he knows nothing about B.
After hearing that Naruto and Killer B fistbumped, knowing Killer B, he assumes that he must have something planned for Naruto. Motoi takes Naruto to the Falls of Truth, where Naruto would come face-to-face with his evil self, but see no way to beat him. Motoi then tells Naruto that he is in no position to ask favors of B, revealing that he once tried to kill him. Motoi is later attacked by the Giant Squid of the island, and to his awe, is saved by Killer B. Motoi at long last apologises for trying to kill him, and B's response was that the only Motoi that he knew, was the Motoi that was his best friend. They shared at heartfelt fistbump, and Naruto, Motoi, and Killer B are all happy. That is when Killer B guides him, and Naruto is peacefully able to conquer his evil self.
During Naruto's special training from Octopops, he finally learns to tap into the Nine Tails' power, activating Tailed Beast Chakra Mode. Having done so, he gains the quirk of Kurama, which is to sense malice, and senses the presence of Kisame Hoshigaki, who had been hiding within Samehada, the blade Killer B stole from him when he was "killed". Kisame attempts to escape, and while he did manage to, it led to a chase with Killer B, confused as to why he was still alive since A and B beheaded him.
Elsewhere, Motoi leads Might Guy and a shinobi named Aoba to the Falls of Truth, where they unexpectedly meet Kisame Hoshigaki as he bursts out from behind the waterfall. Guy mistakes Kisame for his evil self due to Motoi telling him that the waterfall projected a person's dark form, but Motoi realizes who he is. Motoi warns them to get him before he escapes and becomes out of Motoi's range to track. In an intense underwater battle, Guy releases an ultimate never-before seen technique called Hirudora, to counter Kisame's Super Water Shark Bomb Jutsu. Guy's technique overpowered Kisame's and he successfully apprehended Kisame. Before they could prevent Kisame from delivering his intel that he'd gathered while stalking Killer B to the Akatsuki, he commited suicide.
With Kisame dead, they failed to retrieve the intel, as Kisame hit them with a Water Style Jutsu from beyond the grave, and a shark he summoned before his death swam away with the intel. Motoi summons an owl to send to Raikage A. His messenger owls were later used to message the Kage of Yamato's capture by Kabuto, despite Motoi saying that ambush was unlikely since the island never stays in the same coordinates.
Now that Naruto sensed the malice of war and went off to fight, early in the war Motoi was sent to support Naruto and Killer B. Motoi was shocked to see that Blue B was reanimated, and he helped Naruto and Killer B fight Blue B in his Eight Tails state using Lightning Style: Spider Web to temporarily halt the former jinchūriki, protecting Killer B. He showed a degree of selflessness, not caring that the monstrous enemy then tossed him aside, caring more about the protection of Killer B.