Two years prior to the chapter, Plusle, along with Sapphire's Minun, was owned by a passenger on the Abandoned Ship. After their owner's death, Plusle and Minun became wild Pokémon and made the Abandoned Ship their home.
When Ruby arrived on the Abandoned Ship in Adding It Up with Plusle & Minun I, Plusle and Minun began attacking him as a prank. When Ruby managed to discover the two pranksters' identities, Plusle and Minun used their cuteness to lure Ruby into a false sense of security before continuing with their antics. After seeing through their pattern, Ruby realized that Plusle and Minun were attempting to keep him away from a room, which he assumed to be holding a rare type of Berry. When Ruby attempted to open the room's door, he was attacked by Tabitha, a member of Team Magma, who aimed to take the Scanner held inside. Plusle and Minun attempted to stop Tabitha, but were easily defeated. Ruby and Sapphire team up with Plusle and Minun and use them to battle against Tabitha and Courtney. Through teamwork, Ruby and Sapphire manage to win the battle and escape, but lose the Scanner to Tabitha and Courtney. Afterward, Plusle and Minun say their goodbyes as Ruby and Sapphire head off to continue with their journeys.
Plusle and Minun eventually arrive on Mirage Island, where they encounter Ruby and Sapphire in With a Spoink in Your Step II. They decide to assist Ruby and Sapphire by joining their teams and training with them to master Double Battles. Once their training had finished, Ruby and Sapphire leave Mirage Island and prepare to head to Sootopolis City in order to stop the clash between Kyogre and Groudon. Due to worrying about Sapphire's safety, Ruby shoves Sapphire, Plusle, and Minun inside Wallace's aircar and locks them in. He then goes off to stop Kyogre and Groudon, leaving the three behind.
Although Ruby succeeds in stopping the fight, he is attacked by Archie and Maxie shortly afterward. Plusle and Minun use their electrical attacks to try and open the barrier created during Kyogre and Groudon's battle, but are unable to make a hole large enough. They are assisted by the arrival of the Trick Master, who uses the New Mauville generator to boost Plusle and Minun's powers, giving it the strength needed to make a hole large enough to travel through.
After Ruby and Sapphire defeat Archie and Maxie, the two Leaders steal Wallace's aircar and use it to make their escape. By using Plusle and Minun, Ruby and Sapphire trap Archie and Maxie in a giant electrical sphere, finally defeating them.
Like Minun, Plusle is a mischievous prankster and loves to play tricks on people. The two of them are very loyal to their old Trainer and stayed on the Abandoned Ship in order to keep his device safe from others. After joining Ruby, Plusle stopped playing tricks on him and became more focused.