Wouldn't his favorite 5-yen coin be the one that dropped when he came came to Haru to explain the misunderstanding about him being a girl? It got some focus back then and in a few following chapters.
So I was binging this and on earlier chapter I thought, "the money shouldn't came from nowhere tho if i'm a japanese god watching over them, i would pay them for the sugar." I never thought this would be a real thing