Fire Pokemon
Ninetales
Caught as a Vulpix; found on Route 7
Level 55
Female
Nature: Gentle
Characteristic: Good Perseverance
Move Set: Flame Burst, Inferno, Fire Blast, Sunny Day
This Vulpix came to Atem when he was just in his early second year of training, a very dark time for him. She'd wandered onto him in the middle of a storm and was determined to keep the boy from freezing to death. Through the night she valiantly kept a flame going and nudged Atem to make sure he was alright. At one point she'd even brought an apple for him to snack on. He's been grateful to her ever since, always regarding her as a refined sort of mother figure to his other pokemon as well.
Arcanine
Caught as a Growlithe; found on Route 37
Level 56
Male
Nature: Quiet
Characteristics: Likes To Run
Move Set: Fire Fang, Flamethrower, Heat Wave, Flare Blitz
This young puppy ran into Atem while on a run with its pack. Atem stopped for a while to play fetch with it, needing the break after a hard gym battle. The two bonded very quickly after that. Though of course they went through a battle before Atem was allowed to catch the young dog and add him to his team. Arcanine often loves going for runs after battle, especially once he's come back from the pokecenter. Instead of letting Atem ride atop him, though, he secretly enjoys taking off before Atem can hop up on him and making his master take chase after him.
Rapidash
Given Ponyta
Level 70
Female
Nature: Sassy
Characteristic: Somewhat vain
Move Set: Flame Wheel, Stomp, Inferno, Flare Blitz
Atem was given Ponyta as his very first pokemon when he was young by his parents. The two became fast friends, Atem loving to brush and take care of her coat (and Ponyta loving to be taken care of). The two rode all over town, sometimes causing mischief with the locals. She was his very first pokemon and has been with him from the very start of his journey. An unusual starter but one he'd never give up for anything. He still loves to ride Rapidash at top speeds over the regions, the horse loving to carry him about and challenge him to hold on tighter... as long as there's a nice long brushing in it for her later.