same way you caught tapu koko! only, i didn't "re-do" everything for each one, no i just battled each one when i arrived at there spots and caught them!
I actually found blaziken as a torchic, almost beaten to death by terrible trainers, i quickly killed them and took care of torchic and when he was all better, i was going to let him go but when i tried, he wouldn't go so i kept him
