Incidentally, it's an old anime trope for the reason for osananajimi (childhood friend) romantic interests is that the boy bought the girl a cheap toy ring at a festival fair like this with a childhood marriage promise.

NWSiaCB said:

Incidentally, it's an old anime trope for the reason for osananajimi (childhood friend) romantic interests is that the boy bought the girl a cheap toy ring at a festival fair like this with a childhood marriage promise.

That makes it even more painful when one party falls in love with someone else in the future.