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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, Koji may have some noble intentions despite his deeds and sinister demeanor, as he seeks to kill Jigen, the world's greatest threat at the time, and even heads back to Kara just to take the chance.
As one of the completely monstrous Inners of Kara, Koji Kashin is an extremely powerful and skilled individual. He was able to kill off another Inner with ease and could defeat Konohamaru Sarutobi, one of the best Shinobi in Konoha, with ease. His prowess and might even earned him praise from Jigen.
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.
Koji is masterful in using ninjutsu from Konohagakure. He is able to summon a large boiler toad to crush Ao to death, have a summoned toad spy on others, and could use the Rasengan as well as erect pillars able to paralyze targets with fuinjutsu. Seemingly as he uses the village's ninjutsu, he is capable of cloaking his presence from the Sensor Division when he infiltrated Konoha. Koji also proves to be skilled 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.
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. Jigen told Koji that he knew Koji disabled the blimp, allowing Kawaki to escape. 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.