The most recent entry in the series, Shin Megami Tensei V, unsurprisingly features the Demi Fiend as an optional DLC boss. It requires the purchase of the Return of the True Demon DLC, though. If you are able to go through the gauntlet of bosses in this DLC, you will face him at the end. Defeating him, though, will not allow you to recruit him as a demon companion.