In the 16thc, portugese sailors came to japan, bringing along with them many new things, like guns,buttons, and more importantly, playing cards.(the cards were an very idosyncratic latin-suited pattern, the most notable feature of which was the fact that dragons or sea-serpents wound themselves around the aces)
The japanese copied this strange new form of entertainment with gusto, down to the very names of the suits, and yes, the dragons. However, with frequent copying, the dragons ( and the court cards too) became more & more stylized, till the extent that they were transformed to splodges or squiggles , what little detail obscured under paint.
later, someone had the bright isea of repeating one suit of the cards 4 times. in the case of the below deck it was the suit of batons, nut others used the suit of coins.
anyway, all the patterns I mentioned above, including the portugese patern, are long extinct. al that is left is this deck.