Hi! I only remember bits of this manga. It was about a boy whose grandfather recently passed away I think and then he received a letter or something saying that he has to pay back a debt to this person on another island or something. It turns out that this person is a prince I believe and that a long time ago the main boy and his grandfather used to go there to help with the gardening. He doesn't really have a debt to pay back it was something the prince made up so that the boy could stay there with him. And that's as far as I remember. All help appreciated! 🙂

Is it Minami no Kuni no Ouji-sama?

Omg yes!!!! you're amazing thanks so much! idk why i just thought of it and felt like reading it today haha 😀