Raising Demonic Beasts, Why Can I Only Bind Fairies?

“Disciple, do you have some kind of grudge against the fairies of Tianyun Peak?” “Um... I’ve never had a grudge with them.” His master furrowed her brows. “Then why are you throwing rocks at their heads?” “I wasn’t throwing rocks.” Bai Chuan looked a little embarrassed. “Then what were you throwing?” “Poké Balls.” His master sighed sadly. As expected, her disciple had trained himself stupid. A perfectly ordinary stone, and he called it a Poké Ball? I transmigrated, and with a pet-raising System, I was destined to find a spirit beast with perfect stats, high base stats, and the ability to tank, hit hard, and heal. I’d max out its training values and give it the best nature, so it could shield me from wind and rain! But why can my Poké Balls only catch fairies?