"You take the wish,"
Taking the wish.
That means participating in the battle. He's trying to make the Prince join the battle
A wish that will be granted to you by the emperor. Some may wish endless amounts of money, more lives, superficial things, more magic and many more.
In his case, that would be...
"Wish to reclaim your throne or unbind your magic,"
Everyone in the room fell silent. No one said anything.
A wish.
He now has a single chance to take his magic or reclaim his throne.
"This only happens for this year's battle, you're never going to have another chance like this," Ethaniel says. "This is considered the most valuable prize ever offered in this battle. You have to participate."
"And how well do you think the emperor can do that for me?" he suddenly asks. "We searched all places to unbind my magic, Ethaniel. We found nothing."