The second button down from a high school jacket, classically the gakuran. The button is customarily given by an older boy to a younger girl upon graduation, signifying affection - the idea being that the second button sits closest to the heart.
The buttons are typically brass-toned and embossed, it may look simply like a coin once removed from clothing. If it can be inferred from wider context that it's a button from a jacket or shirt, this tag should be used.
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