SFL-2000P1 Control Unit
According to CD AGES (current? owner of this unit) "Dreamcast Model SFL-2000P1 Control Unit. These were designed to run "Hundred Swords" at select Sega Centers in Japan." Considering the "SFL" model, the microphone input, and how it resembles an unpolished Sega Fish Life I feel like these were just Sega Fish Life test units that were re-purposed.
It looks like it has a standard Dreamcast motherboard. A/V connector goes to the video out PCB. Serial connector goes to a serial port PCB with what look like some voltage level converters to work with RS232. There's a separate Maple Bus board that looks like it has the IC used in Dreamcast controllers, which is connected to that SIP board. The Maple Bus board is also connected to the DIP switch PCB, it looks like DIP switch PCB also has some buttons.