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Rauji Ooyama is a member of the Shimon Famiglia. He previously attended Shimon Middle School, but he and his Family transfered to Namimori after an earthquake hit their area. They chose Namimori because it is relatively earthquake free and they are invited to the Vongola Decimo's Inheritance Ceremony.
Rauji is a quiet character who tends to only speak when spoken to. He is very agreeable and also considerate, shown when he offered to walk Enma home because Enma often gets bullied. Rauji also doesn't mind taking orders from others, as he didn't care about being Lambo's subordinate. He was also the only one of the Shimon Famiglia that appeared to have regretted taken Sin, as he was the only one with a frown on his face. Later this is shown to only be a facade used to hide his true cruel personality.
Rauji, along with the other Shimon Members, except for Julie, watches Adelheid and Hibari fight on the rooftop of the Namimori Middle School and says that Adelheid got her self into some trouble. He was fairly surprise that Hibari was able to push Adelheid across the rooftop. But fortunately, Reborn was able to stop the fight by pushing Tsuna between the two. Reborn says that the Shimon are the Vongola's guests for the Inheritance Ceremony, Reborn even states that the Shimon Famiglia has been their ally even before the time of Primo, but he did not know of them because they have become weaker over the generations. Which shocks everyone one of Tsuna guardians. Adelheid, however, responds that they will attend school normally, without any interference. After Gokudera heard that Tsuna was attack by a hitman, he calls a meeting between the two families. Rauji is seen with other Shimon Famiglia members expect for Julie, P. Shitt, whom Adelheid says is meditating and Vongola Guardians in a restaurant, discussing about how to protect Tsuna during when the Ceremony comes in way. But before arrangements could be made, Adelheid says that they need to discuss this with the other members, who are not here.
At the Shimon Famiglia hideout, Adelheid proposes protecting the Vongola Famiglia, but in their own way. Everyone agrees with the idea, Adelheid also asks everyone "has any one taking good care of "that"?", in which Rauji and everyone else responds as a yes. She then asked Enma to show them the Ring that proves that he has the inheritance to be the Boss of the Shimon Famiglia. The Shimon Family later told Tsuna that they will guard him while eating breakfast at his house along with Rauji and Koyo. Each of them will stay in his house to guard him, with the first day being Koyo's turn. Lambo who has already taken a liking towards Rauji, is grouped with Lambo to patrol Namimori Park to protect Tsuna. Later, to Tsuna's surprise, Rauji casually agrees to work under Lambo. He and the rest of the Shimon Family are seen at the at the hospital with the others about Yamamoto's condition after he was attacked in the baseball locker room by Kaoru Mizuno. Koyo also tells them that they no had leads, but was interrupted by Reborn, who said that he had found a lead. This news surprised the Shimon Famiglia, but Reborn said that he couldn't share it with the Shimon Famiglia since it involved "secret information about the Vongola." The next day he is seen at the Vongola Inheritance Ceremony with the rest of the Family. Rauji and the rest of the Shimon were all surprise to see Yamamoto heal from his wounds, but they didn't say anything about it. He is later seen amongst the crowds during the ceremony waiting along with the rest of the Shimon Famiglia, when Tsuna was to receive the Vongola Sin from the Ninth. But before the Ninth could have gave Sin to Tsuna, an an explosion is heard.
The Ninth revealed that the Sin in the ceremony was merely a fake. He proclaimed that the real one was in a safe that was impossible to penetrate. Suddenly, the safe was broken open, revealing Rauji and Enma with rest of the Shimon. Enma stated that they came to the ceremony to take back "Sin" for the Shimon Famiglia, and get revenge on the Vongola.Tsuna asked Enma why they attacked Yamamoto. Enma reponded that he was a Vongola Guardian and it was a "rightful atonement." Enma then went on to explain that the Sin belonged to the Shimon Famiglia and that it was the blood of their First Boss. Enma declared that he will inherit their family as the Tenth Boss and take revenge on the Vongola by gathering Mafia from all over the world and standing above them as their leader. The purpose of the war was to gain back the pride of the Shimon. Rauji and the others then released their rings as Enma said that the reason that Vongola Primo got rid of the Shimon was because they had a power that rivalled the Dying Will Flames Of The Sky, which were the Dying Will Flames Of The Earth. Enma then went on to defeat Tsuna and his Guardians. The Shimon Famiglia then took their leave and went back to their home.
He later seen again along with Enma and the others when Tsuna and the others arrived at Shimon island, then at the meeting with remaining guardians of Shimon regarding the result of the fight between Ryohei and Koyo and about the memories of Cozart and Giotto, and lastly when Lambo fell to the pitfall, he appeared before Lambo, seemingly ready to fight him.
Rauji tells Tsuna that the dome is held up by the strength of the walls and if Tsuna manages to break out, the dome would fall apart and Lambo would be trap beneath. He tells too that the surrounding rocks are rich with minerals and crystal, causing and ideal location for his abilities saying that Fighthing there would be a simple victory for him.
Lambo ignores Rauji and tells him that he's his master and must obey him. With anger Rauji says that he's Lambo's slave no longer. Lambo stills thinks it's a joke and laughs. Rauji, very angered, stomps on the floor without intentions of letting Lambo live. Because of this, Lambo cries and he upgrades his old Vongola Gear and it transforms into the Lighting Helm Version X. Lambo says that the helm is too tight. With this, Rauji says that they are gonna fight like sumo wrestlers and whoever falls from the dome is the loser. Rauji attacks Lambo and seemingly knocking him out of the dome and says that he's the winner because even if he survived that fall, Lambo is out of the dome. He then laments that if Lambo had not been a Vongola and were a few years older, they could have been good friends. However, the dust settles and 15-year-old Lambo is standing there holding the Helm and claims that from now on they are the same age. The real battle then begins. Rauji then explains that he is the guardian of the Mountain just as Lambo combines with Gyuudon for his Cambio Forma.
Abilities and Weapons
- Mountain Shimon Ring: Rauji also possesses one of the seven Shimon Rings sealed by the Vongola Sin. When activated, it turns into a weapon. When activated, his ring becomes armor on his arms and back. The armor is able to open up and release mountain flames looking similar to wings on a beetle. It is also able to form armor over his jaws which he is able to concentrate his flames through. This flame can be compressed to resemble rocks and then by covering them in flames to somewhat resemble magma. This creates two horns of flames extending from the armor on his jaws similar to horns on a stag beetle.
- In the Reborn! Fandom, his number is 62.
- He gets along well with Lambo, going so far as to agree to stay longer so they could play more.
- He calls Lambo "Lambo-san."
- His surname literally translates to "Large Mountain," fitting his large and bulky appearance, as well as his choosing a battlefield modeled after the mountains where he claims the Vongola began their betrayal of the Shimon and his flame.