Crown Summon of Elves

Why don't the trainers of this world use Poké Balls? Why can they use Giga Drain? Why do I, a Champion trainer, have to go to Modu for university? Bai Xuan looked at the somewhat fantastical summoning array in his hand, pondering for a long time - it seems not using Poké Balls is also fine. The Pokémon shouted in unison: "Good or bad doesn't matter, Master, when will you summon us?" Bai Xuan waved his hand calmly: "What's the rush, my wife and daughter haven't arrived yet."