Diamond

Diamond first appeared at the New Generation Funny Grand Prix in Jubilife City, where he, along with Pearl, was awarded the Judges' Special Merit Prize. Upon leaving the Grand Prix with their prize, Diamond and Pearl bumped into Professor Rowan and his assistant, Mr. Berlitz, causing them accidentally switch envelops and, unknowingly, receive the mission to guard Platinum Berlitz on her journey to the top of Mt. Coronet, although they believed they were on a reality show and Platinum was the host.

In Oreburgh City, Platinum decided to challenge gyms, and Diamond and Pearl helped her train, which helped build trust within the young trio. At the Valley Windworks, met up with Mars for the first time and defeated her with Diamond's emotion and kindness. After many different trials and crises together, they finally reached Mt. Coronet, but they soon discovered that the cavern they have entered would not lead to the summit, and therefore had to continued their journey on to the eastern side of Sinnoh.

In Hearthome City, Platinum decided to challenge a Super Contest. While Pearl helped Platinum practice, Diamond began cooking Poffins. When Platinum was about to quit the contest due to her being attacked by the other participants, Diamond cheered her up with a piece of pie, which allowed her to continue and win.

Afterward, the trio was attacked by Platinum's true bodyguards, Paka and Uji, who believed that Diamond and Pearl where kidnappers who had taken Platinum for ransom. Thankfully, they were saved by Fantina, who took them to the Lost Tower. Once Fantina deemed it save for them to leave, the trio went to the Solaceon Ruins, where they saved some Unown before heading back out on their journey.

In Veilstone City, Diamond and Pearl met up with Paka and Uji for real and had their first true battle with Team Galactic. During this battle, Diamond's Wig and Pearl's Monferno both evolved and Platinum's true identity was revealed to the two boys by Paka and Uji. However, before her real bodyguards had a chance to meet and explain things to the girl, they were banished into another dimension by Saturn. Once this happened, Diamond confessed to Pearl that he knew Platinum wasn't a reality TV host from the beginning, but he had kept it to himself because the misunderstanding was the thing that created and held together their friendship. The two then took an oath that they would protect her and keep their real identities a secret.

Later, following a seperation from Pearl at Lake Valor, an adventure in the Great Marsh and Platinum's gym challenge i Pastoria City, they met up with Cynthia at the Pokémon Mansion, and she helped them clear the group of Psyduck that were blocking Route 210. They encountered Cyrus again in Celestic Town when the man broke into the ruins that held Sinnoh's legend of the three lakes. After the showdown with the man, in which Diamond and Pearl had a huge argument that had nearly cost them the victory, the trio ended up in Hearthome once again and Platinum challenged Fantina, who turned out to be the gym leader of the Hearthome Gym.

After gaining a victory, the trio learned of Mr. Berlitz and Professor Rowan had disappeared. In order to find them, the trio went to Canalave City, where they mistook Byron as Mr. Berlitz and Professor Rowan's kidnapper. During the battle between the young trio and Byron, Diamond befriended Byron's Shieldon. After realizing the whole thing was a misunderstanding, Platinum finally learned of Dia and Pearl's true identity, and was completely horrified by the shocking news. However, after a horrible night full of nightmares, she decided to keep the boys as her companions and they resumed their journey with the new goal to stop Team Galactic's evil plans.

The trio was then split up to defend the three lakes of Sinnoh and Diamond was assigned to go to Lake Verity. However, Byron didn't believe that Diamond was a strong enough battler and made him go through training with Riley on Iron Island. During this, he learned to overcome his weakness in speed.

Soon, Diamond was back in Jubilife City, where he saved the President of the Poketch Company from wild Lickitung, which evolved into a Lickilicky during the battle and joined Diamond's team. Afterwards, he arrived in Sandgem Town accidentally found himself in the Berlitz's Mansion and was mistaken as a thief by Platinum's butler, Sebastian, but this was quickly taken care of and explained. Before resuming his quest towards Lake Verity, he fought off a swarm of Yanmega that was sent by Team Galactic to attack Professor Rowan's Science Lab.

Diamond then made one last detour and returned home to find some winter clothes that his mom bought him, finding a note left by his mom telling him that she heading to Lake Verity to get some berries. Upon reading that, Diamond realized that his mother was in danger and rushes out of his house to the nearby lake, where he find his mother being held hostage by Mars.

Diamond and his Mom fought off Mars and Diamond went airborne on Drifblim. However, after Mesprit was awakened, he followed Mars onto the Team Galactic Air Shuttle and found himself back in Veilstone City. There, he infiltrated the headquarters of Team Galactic and was soon reunited with Pearl and Platinum. They then save the Lake guardians by sacrificing their Pokédexes.

The newly reunited trio then regrouped with Cynthia and headed to the Spear Pillar, where Diamond and Pearl split up with Platinum and Cynthia and time and space begins to distort. As the two boys began to fight Dialga and Palkia, they were ambushed by Cyrus, who commended them from for trying to stop him.

This angered Diamond, who then verbally attacked Cyrus by stating what he believed Time and Space was. Cyrus then had Dialga and Palkia attack the boys but the man had troubles controlling them as one of the Red Chains that had been used to control the Deities had been destroyed by the Gym Leaders. Platinum then returned and revealed that the way to defeat Cyrus was the power of balance and, when Cyrus' control over them wavered, the three released the Dragons from their constraints. The Dragons then used their powers to create a sphere that distort Cyrus within it. The three then celebrate with a fist bump.

Pokemon crimson
In Pokemon crimson Diamond travels to the battle tower in Larouse city along with Pearl, there they meet Andre, Platinum and the others. Diamond seems to not like Andre due to him believing that Andre and Platinum have feelings for each other since they teamed up with each other.