Nice finding!. I don't know the purpose, Google translate sucks. HDMI, video teloper who knows maybe that board is not 100% functional... we need a japanese user to get a proper translation. Interesting site there are pictures of several relatively unknown hardware like the Neos MSX2 Version Up Adapted cartridge, robots, etc
As for the description seems to be initally a "Video developer and superimposing cartridge". Also mentions the possibility to generate HDMI output and network connectivity aswell.
