Early History[]
Not much is known about Diego's life before Yami other than the fact that he is quite wealthy, and that he was once a professional masked wrestler. It is unknown how and why he stopped Masked Wrestling, but it was around this time that he joined Yami and became a member of the One Shadow Nine Fists. A couple of years after this he meets Rachel Stanley and takes her as his disciple. He also participates in the joint training of Sho Kano as the sole successor of Yami.
Plot[]
'DofD Tournament Arc[]
Diego is the sole representative of the Nine Fists in the D of D and acts as the tournament's referee. His belief in a man's romance of trespassing
Diego Irritated
allows the Shinpaku Alliance to participate.
Diego, as the referee, tried to stack the tournament against the Shinpaku Alliance, but he was so impressed by the showmanship of Siegfried's entrance that he more or less ceased his crooked officiating.
Master-Disciple Tag Match Arc[]
Diego and his disciple, Rachel Stanley, have, unbeknownst to the other members of Yami, made preparations for Rachel to fight Kenichi. The said plan involves inviting Kenichi and the master of his choice to a tag team battle against Rachel and Diego. Refusing the challenge or bringing an additional master would result in a bomb being set off. He is surprised to find Renka arriving with Kensei but seems willing to go on with the battle. However, it is later revealed that the true show is the soon to be explosion of the ship, described as his "Murder Show".
Upon a fiery backlash by the enraged Ma Kensei, Diego loses his composure and takes off his "Smiling Mask", only revealing there to be another mask underneath. This shocks Rachel and causes panic among several of the audience; and Ma Kensei refers to this as Diego's true face; "Angry Steel Fist". Upon this state, Diego battles with Ma with powerful, ferocious attacks, even bringing the battle out of the ring and apparently not caring for the safety of his precious audience in the brawl. It is revealed that he no longer regards these people as 'audience', as they are targets on Yami's list of elimination. The real audience gathered in ships further off, watching the battle via real-time screening.
Diegos tried to keep Kensei in the air, claiming that there is nothing a Luchador can't defeat in the air. However, he is defeated when Kensei got back on the floor, saying that the earth belongs to Chinese Kung Fu. Afterwards, his plan was thoroughly foiled, with the intervention of Miu, Kenichi and Furinji Hayato. At the point of defeat of the climax of the battle, he took care to make sure the camera angles were all fixed on him till the end and declared that it was 'Diego Quality' for him to even lose spectacularly. He offers his mask to Kensei, comically revealing a third mask, and asks to be killed, only to be denied, but Kushinada arrives and throws him overboard. He is saved by elder and sent to Big Lock.
The Eternal Sunset Arc[]
After the battle between Shinpaku Alliance and Yomi at the amusement park and the fight between Isshinsai Ogata and Tsutomu Tanaka ended, Diego is later seen again inside of Big Lock with Alexander Gaidar. It is then revealed that both he and Alexander can escape Big Lock anytime they want and are staying there willingly because of their pride as martial artists and because they have to obey the winners orders only because they lost to Ryozanpaku fair and square. They stated that they will leave Big Lock only when they have a reason to get out, to which the Yami weapon user told them that the Hachiou Executioner Blade team is gathering again, a statement which intrigues them both. After hearing this the weapon user stated that the One Shadow wanted them to know this and to think carefully about their decision. He is next seen later still in Big Lock, where it is revealed that both he and Alexander have been sneaking out of Big Lock to buy various items out of boredom. He talks to Alexander about how his disciple has found Big Lock and has been waiting for him all this time, then starts to wonder if his disciple, Rachel misses him at all, to which Alexander mockingly asks Diego if he is homesick. When the guards demand Diego give back his posessions, he does so while going through an electric field and warns them if they keep harassing him he's liable to snap.
During the Eternal Sunset with Yami and Ryozanpaku, Diego and Alexander escapes from Big Lock. As the battleships prepare to head out a soldier reports seeing shadows in the water as three of their battleships are sunk. A submarine surfaces with Diego Carlo and Alexander Gaidar inside, who have been guided there thanks to Boris. Both masters arrive to fight along with Ryozanpaku as Diego asks his disciple where he can stand out the most and Alexander wishes to maintain the honor his deathmatch with Akisame and stop Yami's "inelegant" methods.
Fighters arrive to engage the two masters and Diego is accompanied by Meatman and a film crew, preparing to broadcast his battle so he can stand out. Diego asks Alexander why he is fighting against Yami, and he answers that if there is no beauty in the Eternal Setting Sun then it must be stopped, as he charges in and mows down a group of soldiers.
Once the Eternal Sunset is lost, Diego celebrates with Alexander.
Epilogue[]
In the Epilogue, Diego, now pardoned for his bad crimes, goes back to masked wrestling alongside Rachel.