The typical isekai story... but the MC is not the one isekai'd, wait what?

So, the fantasy mediaval world with isekai heroes summoned into this world, but this time main character is not the chosen one. Main character, Cedric, is a prince instead! But do you think he is the one to become the next king? Wrong, his three older brothers are in line already, just waiting to get the right for the throne.

What about out pratagonist then? He does not care about the politics, he just seeks... freedom. Cedric wants to be a simple adventurer - a traveling mercenary. After he had to watch isekai'd heroes do all that and more, why can't he?