Responses
Hm, I'll have to check the raws for the first chapter. Perhaps the Japanese said "relatives" and the original translator decided to use the word grandparents.
SPOILER:
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Needless to say, Kou's grandparents never show up in the manga, including the rest of the chapters.
I looked back on the chapter one raws, and it's a mistranslation by the original translator. It explicitly says that he lived with his uncle.
Thanks for clarifying that.
But now it seems he lived with his jerkass aunt,uncle and cousin? Was the grandparent bit a mistranslation?
Anyway, Gin is such a good friend, and Kou was too nice to those people, but I guess he'll shut them up with fireworks display