There are so many accessories for the Sega Saturn that people in the west just never got to see. One of the most obscure is the Saturn's Midi interface unit. This unit made by Waka Interactive Entertainment came with their Saturn Software titles, Saturn Music School and Saturn Music School 2. Waka also make the only Midi compatible software for the Dreamcast being O.TOI.RE. however in that game's case you had to buy the Sega made Midi interface from Sega's online store. Needless to say that it's very rare. Far more rare than this Saturn Midi interface unit.
The Midi interface unit was used to connect your midi compatible keyboard to the Sega Saturn for use with the Saturn Music School software. Here you could learn how to play the keyboard as well as be judged and ranked on your abilities. The software is very good (especially the second version) for beginners to get in to keyboard playing and well worth tracking down even if it's just for this Midi interface unit.