Pokémon Adventures, Vol. 15 by Hidenori Kusaka

Ruby's father Norman is the new Gym Leader of Petalburg City. But Ruby doesn't want to follow in his father's footsteps - he wants to win Pokémon Contests! Sapphire's father Professor Birch is the local Pokémon researcher. But Sapphire is tired of gathering scientific data - she wants to win Pokémon Battles! When Ruby and Sapphire meet, they're more likely to hit each other than hit it off. But then Sapphire challenges Ruby to a competition! Which of them will achieve their dreams in just eighty days?! Meanwhile, what dastardly plan is Team Aqua up to...and how does it involve Sapphire?!