Pocket Hearts: Birth By Sleep (KH crossover)
The first time that portals leading to other worlds was ten years before Eric, Barry, and Paul went on their first adventure, and three Keyblade wielding Pokemon Trainers from Unova: Travy, Ogon, and Voda, under the orders of Master Eraqus and Master Xehanort, go to the first portal, leading to the Land of Departure, to receive Training to earn their potential title of Keyblade Master. However, creatures formed from fledgling emotions, the Unversed, have been popping up in other worlds, and Eraqus sends them to investigate.
[*fun fact: the main character's names are Russian for Grass, Fire, and Water respectively, and reflect the type out of the trio they DON'T have as any Pokemon].
Travy is equivalent to Ventus, and prefers quick attacks over any other. His first two Pokemon are Samurott and Simisage. Voiced by Joshua Seth.
Ogon is equivalent to Aqua, and a gifted mage. Her first two Pokemon are Serperior and Simipour. Voiced by Lani Minella.
Voda is equivalent to Terra, and uses brute strength to his advantage. His first two Pokemon are Emboar and Simisage. Voiced by Austin St. John.
(Note: I will focus on one character's story at a time. I will make a poll which will end next week to see which order I will go in.)
The three friends' fates are intertwined, and arrive at the different worlds at different times, but sometimes all meet up.