Mr. Briney, who grew old and alone at the old docks in Rustboro City, was one day visited by a Wingull. Peeko approached Mr. Briney and soon befriended the old man.
One day, May visited Mr. Briney, whose Peeko was slightly scared of her. May offered Peeko food and befriended it by stroking it. However, a Team Aqua agent came to Mr. Briney and threatened to have his Crawdaunt hurt Peeko. Mr. Briney was forced to lie to May and refuse helping her. Mr. Briney was also forced to show the agent a ship to sail away. The heroes came to visit Mr. Briney, though the Aqua Agent came and showed Crawdaunt had captured Peeko. Team Rocket also arrived and tried to snatch Crawdaunt, but took Pikachu and Peeko away. Brock's Lotad managed to blast Team Rocket away, though Peeko was captured by Crawdaunt once more, who went onto the Aqua Agent's ship and sailed away. Fortunately, Mr. Briney built a ship looking like Peeko, so everyone sailed and intercepted the Aqua Agent. While Mr. Briney retrieved Peeko, the Aqua Agent went into Team Aqua's submarine. The following day, the heroes, Mr. Briney and Peeko sailed towards Dewford Town.
They stopped at a small island, where May and Max went swimming. However, the group was attacked by wild Sharpedo, so Peeko rescued May and Max, flying towards the coast. After devising a plan, Taillow and Peeko pulled Ash away, who stood in a can, which distracted the Sharpedo. In the end, Mr. Briney, who took the heroes to Dewford Town, waved goodbye with Peeko and sailed to Slateport City.
None of Peeko's moves are known.