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Koji Kashin (in Japanese: 果心居士, Kashin Koji) is a member of Kara and an antagonist in Boruto: Naruto Next Generations. He is a member of the inner group within Kara.
Koji Kashin is an ambitious individual who is willing to commit acts that go against what Kara wants. He has an individual mindset and acts on his own terms without fear of going against Kara. Unlike the other members, Koji acts secretly and like the leader does not prefer for his plans to be known to too much people. Koji is also ruthless as shown by how he killed his own team member and by how he murdered Ao. Koji is also interested in Boruto Uzumaki and is shown to be calm when he allows the Leaf ninja to take away Kawaki, whom he needs to retrieve.
However, despite his deeds and sinister demeanor, Koji does have noble intentions and is loyal to humanity as a whole as he seeks to kill Isshiki Ōtsutsuki, the world's greatest threat at the time, and even heads back to Kara just to take the chance. His loyalty to Kara and disdain of shinobi being a facade from the beginning, Koji is shown to be proud of being a shinobi, stating that he is content with being a tool because that is what a shinobi is, and is shown to be extremely brave, as despite knowing that he stood no chance against Isshiki's full strength, he valiantly fought to the end, with even Isshiki commenting on Koji's bravery. It is, however, indicated that he may have been attached to Amado, his creator, as Isshiki noted that despite Koji's gallant efforts to defeat him, part of the reason why he was so resolute to defeat him was because he knew Amado had left him to die and deemed it unprofessional for a shinobi.
As one of the completely monstrous Inners of Kara and a clone of one of the Legendary Sannin Jiraiya, with extensive modifications of Shinobi-Ware, Koji Kashin is an extremely powerful and skilled individual. With just his natural skill, he easily killed off fellow Inner Victor and could defeat Konohamaru Sarutobi, one of the best Shinobi in Konoha, with ease. His prowess and might even earned him praise from Isshiki, who acknowledged him as being very capable. Although he was no match for Isshiki even in Jigen's body at full power, he was capable of killing him when he was still weakened from his battle with Naruto and Sasuke and even temporarily holding his own against the fully reincarnated Isshiki, though was still soundly defeated and Amado noted while he trusted Koji with killing Jigen, he had no chance to defeat Isshiki.
Koji is shown to be extremely stealthy and fast, able to sneak up on the experienced elderly Inner of Kara with ease, even mocking him, and could move around Konoha completely unnoticed. He is also quite agile, able to jump into the air and immediately balance himself to counter Konohamaru's Rasengan with his own, and displays great taijutsu prowess, able to easily counter all of Konohamaru's attacks and outmaneuver him enough to place a toad on him completely unnoticed. When fighting the weakened Isshiki in Jigen's body, he was shown to be able to contend with him, able to counter and exchange blows with him reasonably evenly, and also proved to be fast and agile enough to quickly get behind Isshiki just as he had finished absorbing his fireballs to attack him. He also displays incredible resilience, as he was able to quickly rebound from being kicked by Isshiki fully using Jigen’s Kama and withstand having his mask shrunk to his face’s molecules without any damage, continuing to fight against Isshiki, even surviving being crushed by three pillars, which destroyed his arm, crippled his legs and torso, and still had enough strength to summon a toad to escape. While in Sage Mode, he was temporarily able to hold a strike from the fully reincarnated Isshiki at bay for him to attack and withstand being overpowered in said clash and punched in the face with only minimum blood.
Koji has extremely large reserves of strong chakra, as he was able to easily use multiple advanced techniques in his battle with Jigen until he killed him and then go on to use Sage Mode against Isshiki, using many powerful techniques, while still having enough strength upon his ultimate defeat to perform the Summoning Technique and escape.
As a clone of Jiraiya, a famous master of ninjutsu, Koji is likewise highly proficient in ninjutsu, especially Konoha's style, being even more adept than his genetic template. He is proficient in mind-probing and Genjutsu techniques, able to keep Katasuke Tono under the influence of Genjutsu for an extended period of time, altering his personality, and extract information from Katasuke regarding Scientific Ninja Tools, and is masterful in using the Shadow Clone Technique, able to create multiple clones and seamlessly switch places with them to avoid detection, which could even catch Isshiki off-guard. He is also capable in Fuinjutsu, able to erect pillars capable of paralyzing targets, and Space-Time Ninjutsu, able to enter the Ten-Tails' dimension at will and can carve Space-Time Ninjutsu seals to summon eternally burning natural fire from flaming mountains.
Having inherited Jiraiya's skill-set, Koji displays greater finesse and ability with toad-based techniques, capable of using small ones for surveillance or acting as mediums for his techniques or giant ones to crush targets and is able to use the Reverse Summoning Technique to teleport himself and others via his summons to other locations. He also retains his template's abilities to manipulate his hair to attack and defend against his enemies and launch sticky oil from his mouth and is proficient in the Rasengan, easily matching Konohamaru's usage and even capable of using the mighty Ultra-Big Ball Rasengan.
Koji is proficient in Fire and Earth Release. He has shown outstanding, unseen levels of mastery in using Fire Release; he can use True Fire of Samadhi, that from hitting targets through small mediums, will cause the victim to spontaneously combust, strong enough to overcome a target's regeneration capabilities and never extinguish, which he can amplify by having multiple toads together, which even briefly pressured Isshiki's weakened absorption. He can also launch a barrage of fireballs, widespread of flames, or a single large fireball from his mouth. While in Sage Mode, he can even imbue his fist with fire to consume his target in flames upon striking and perform the biggest scale Fire Release technique Sage Art: Five Fire Gods' Fan of Flames, capable of generating overwhelming amounts of flames to the point of giving Isshiki Ōtsutsuki some trouble shrinking them. With Earth Release, he can morph the ground in the area into sinking mud to ensnare his foes.
Koji has mastered Senjutsu to a much greater level than Jiraiya, being capable of using Sage Mode with a perfect balance of chakra and natural energy, symbolized by him gaining yellow, toad-like irides with orange pigmentation around his eyes, which he impressively could achieve in a matter of moments; such a high level of speed was never shown even by Naruto himself. While in Sage Mode, Koji's physical and ninjutsu prowess were enhanced enough to hold his own against and make Isshiki take him more seriously.
Koji Kashin first appears along with the other members of the inner group as they meet to talk about recent news for their group. Koji meets up with an elderly member of the inner group after the meeting and kills him. After some time passes, he approaches Ao to tell him the news that the vessel is missing. He orders Ao to retrieve the vessel. When Ao was pursuing the Leaf ninja in his battle, Koji approaches him to talk to him and remind him that he is doing a poor job so far with the Leaf ninjas and finding the vessel. When Ao lost in his battle to Boruto, Koji appears and summons a giant frog on top of them. Ao saves Boruto but was killed in the process. Koji confronts the Leaf ninja and took a particular interest Boruto for having the Kama seal. Koji got into a skirmish with the Leaf ninja before leaving.
Koji sticks around to watch the Leaf ninja interact with Kawaki. Delta appears and reminds them that they need to retrieve the vessel but Koji tells her that it is not a big deal. The two watch Garō as he fights against Kawaki. Kawaki kills Garō with his Kama power and soon loses his consciousness for using up too much power. Koji tells Delta that it is okay that the Leaf ninja takes Kawaki with them as he is confident he would not tell them important information.
Later, Koji and Delta are standing outside of the Hidden Leaf Village. Koji states that there is a barrier around the village that detects outsiders who try to enter. He then successfully enters the Leaf and tells Delta that only he is able to enter, and she is not. Koji manages to evade both detection from the Hidden Leaf Village and to avoid Delta's barrier. Koji hides in the village and uses one of his frogs to locate Kawaki. After locating Kawaki at Naruto's house, Koji is forced to lay low as engaging with the Seventh Hokage would be too dangerous but he doesn't intend on intervening anyway as he instead plans to seek information and uses his frog to spy on Kawaki and Boruto. When Boruto and Kawaki's hand seals make contact, Koji notices a disturbance and is wary if Boruto might have the same powers as Jigen. Koji notices Delta infiltrating the Hidden Leaf Village and remarks about her recklessness. Koji later notices that Delta self-destructs after losing in her battle to Naruto. Koji comments that while Naruto holds terrifying power, he would not be able to win against Jigen and only Boruto's kama seal has the potential to deal with Jigen's kama seal and powers.
As he continues to monitor Kawaki, Koji is concerned about Jigen not making a move after so long as Delta's defeat has been for quite a long time and he should have learned about Boruto's Kama and Naruto's custody of Kawaki, both of which would certainly necessitate Jigen to personally handle things. To his great shock, Kawaki's Kama suddenly activated and opened a portal for Jigen to arrive in. Koji is perplexed about Jigen's ability to so easily find and reach Kawaki, as if he could just do that, why didn't he do it in the first place and instead gave a mission to retrieve Kawaki. Suddenly, Jigen coldly glared at the toad he had sent to watch over and Koji in haste de-summoned the toad. As he contemplated the events, he realized from the beginning Jigen had been suspicious of him and had set up the whole mission just to see how Koji would react.
After Jigen takes Naruto to another dimension, Koji wonders why Jigen hasn't returned. He doubts that Naruto and Sasuke could have defeated Jigen, but he thinks that Jigen could be weakened. Koji decides to go back to the Kara base to defeat Jigen.
When he returned to the base, he met up with Amado who decided to join him. When they were confronted by Delta, Amado shut her down. Koji wondered if Amado would be able to shut him down to. Koji summoned a toad to reverse summon Amado to Konoha.
Koji confronted Jigen in the Ten Tails dimension. He recorded the discussion to transmit to Amado. Koji initially tried to approach Jigen more subtly but Jigen revealed he knew from the beginning that he and Amado had betrayed Kara and that it was them who disabled the blimp, allowing Kawaki to escape, and questioned his motives. With no use for surprises, Koji attacked Jigen, but Jigen countered, and Koji used a shadow clone to dodge. He then told Jigen that he was specifically created to destroy him. Calling Jigen by his true identity Isshiki, Koji then skillfully used multiple ninjutsu that Naruto attributed to being similar to Jiraiya to combat Jigen and despite initial struggle as despite being weakened, Isshiki still neutralized all of Koji's assaults easily, he eventually caught Isshiki off-guard and summoned natural flames from eternally burning mountains to burn Jigen's body to death to force Isshiki to reincarnate.