From Bulbapedia, the community-driven Pokémon encyclopedia.
Ruby (Japanese: ルビー Ruby) is a character from the Pokémon Ruby-Sapphire manga who first appeared in Something Happened!! Let's Go After Pikachu!!. He is based on Brendan from Pokémon Ruby and Sapphire and is Red's rival.
Ruby has a big interest in Pokémon from Kanto, especially Red's Pikachu. This is also shown in his house where he has a big collection of them.
Red leaves Pikachu and Clefairy alone for a few minutes which gave Ruby the chance to bargain a trade with Pikachu. Ruby distracted Clefairy by giving him loads of food. As Clefairy got occupied with the food, Ruby switched him for Treecko. Ruby than arrives in his house and has Pikachu join in with the other Pokémon from Kanto. Clefairy spies on him after Treecko told Red what happened. To get Pikachu back, Clefairy disguises half of himself as a man and half as a woman to distract Ruby while Tyrogue and Treecko break through the window to steal Pikachu back. When they did the plan, Ruby and Pikachu become surprised about this and the group managed to get Pikachu back and return Treecko to Ruby.