Tru first appeared in Stagestruck Starly, as one of the three Pokémon given to Platinum from Professor Rowan. Platinum sends him out of his Poké Ball alongside Chimchar and gives him a Pokédex for her bodyguards (who will arrive wearing red and green mufflers), and instructs him to give it to whichever one he likes. Matching the description, Tru chooses Diamond as his Trainer and gives him the Pokédex. Right after that, a flock of Starly appear and begin attacking the group, which results in the three starters fighting and defeating them.
In Ring Around the Roserade I, after leaving the Old Chateau, the group meets Gardenia, who somewhat nudges them into challenging her the next day. The three soon begin training with the starter Pokémon when Cynthia walks by and notices that the three are going to evolve. Quickly after saying this the three evolve, with Tru evolving into a Grotle.
In Passing by Probopass and Maneuvering around Magnezone, the group enters Mt. Coronet and encounters the leader of Team Galactic, Cyrus. He has his Probopass attack them with a powerful Rock Slide for being "noisy" around the site of his Nosepass and Magneton's evolutions, and Pearl and Platinum become trapped under the rubble. The Luxio they met before shows up and uses his X-Ray vision to find the two that were buried, and has Tru and Lax use Tackle to help break the two out.
In Stunning Staravia & Stinky Skuntank II, Tru fights against some Galactic Grunts in order to stop them from capturing Platinum. He starts by using Razor Leaf to block his opponents view and attack at the same time, impressing Paka and Uji. With their advice Tru uses Stealth Rock to assist Chimler by making a platform for him to reach the middle of the battle. Chimler uses a spinning Ember, defeating the group of Staravia. The two then evolve into Torterra and Infernape and the group flees to the top of a building with a satellite dish on top of it. With Paka and Uji's guidance Chimler attacks wildly with Ember and Tru attacks with Earthquake, causing the satellite dish to fall on top of the Grunts. Pearl then realizes that Chimler's random attacks forced the Grunts into the spot behind the satellite and weakened it at the same time. With Tru's Earthquake knocking it down the Grunts had nowhere to run, trapping them.
In Bombastic Bibarel & Heroic Hippopotas, Tru is used in a Double Battle alongside Chimler at the Seven Stars Restaurant, fighting against a Trainer's Bibarel and Hippopotas. Bibarel attacks Chimler with Water Gun and Hippopotas attacks Tru with Sand Tomb. The two counter with Fury Swipes and Wood Hammer, knocking out both Pokémon.
In Dramatic Drapion & Crafty Kricketune II, Tru battled two Scientists that were attacking Diamond and Platinum. With his high defense he easily takes the Scientist's Kricketune's attack, but soon falls asleep from its Sing.
In Floatzel and Jetsam, Tru is used in Platinum's Gym battle against Crasher Wake and his Quagsire. The two start by charging each other and begin a wrestling match. After a while Quagsire used its superior strength to pick up Tru and throw him into the water, which also knocked Platinum in as well. In a few moments neither of them surface and Crasher Wake assumes they drowned and calls the battle off. Platinum calls out from the other side of the arena, revealing that they slipped by him when underwater. Tru then attacks with Giga Drain, knocking Quagsire out.
In Lucky Lucario I, Tru is trained on Iron Island by Riley alongside Lax and Don. The three start by battling against Riley's Lucario and are quickly defeated due to Lucario's speed. Despite the loss Riley points out that the three have amazing defense and work wonderful together. After this Riley took the group into a cave and they are attacked by a wild Steelix. Lax and Don manage to hold it down long enough for Tru to attack with Crunch, making the Steelix flee. After the training Tru learned to overcome his weakness in speed and learned a technique called "Dia-Mach-One-and-Only Razor Leaf", which allows him to fire a single Razor Leaf at a high speed.
During the battle against Mars in Mixing It Up with Machamp, Tru was sent out to free Mesprit from Team Galactic. Tru fires a Dia-Mach-One-and-Only Razor Leaf towards the cable connecting the capture device and then immediately follows it up with a regular Razor Leaf, which blinds Mars and her Yanmega. Despite his best efforts Mesprit was still captured and Tru fell into Lake Verity, separating him from Diamond alongside Kit. They were later taken to Pearl by Sebastian. In Chancing Upon Chingling, once Diamond was spotted by the Advanced level Grunt, Chatler returns Tru and Kit to Diamond. Tru then participated with Diamond's other Pokémon to battle against the Advanced level Grunt but proved to be no match for his strength.
In Double Trouble with Dialga and Palkia VI, Tru was used alongside the other Pokémon to battle against the Legendary Pokémon Dialga and Palkia. With the help of Diamond and Pearl's Pokémon and with a combined technique, they were all able to destroy the Red Chains controlling them.
In Unplugging Rotom (Heat, Wash, Mow, Fan, Frost), Tru battled a wild Rotom that Diamond and Pearl were trying to protect. Diamond sent out Tru to battle against it due to it having a type advantage over Rotom's Wash Form, but Rotom continued to switch and attacked with Overheat, Air Slash, and Blizzard, rendering Tru's attacks useless.