This is an item of stationery (paper or writing goods), or other small merchandise such as good-luck charms, mascot straps, et cetera.
In the form of one of the SEELE monoliths, this music box plays "Sin from Genesis." Other selections are also available, linked below--these game-prize items from Sega are something a little different for your collection!
Please note that the photos shown are of a prototype; the production version may vary. Also, items such as this are mass produced and as a result some inconsistencies in finish and painting may occur; these are not considered manufacturer's defects. If you absolutely must have perfection, prepare to do some touch-up work on your own.