Castlevania: The Bloodletting was made for the Sega 32X add-on for the Sega Genesis. It was meant to be released some time between 1996 and 1997 before the project was scrapped, and much of the team was moved to work on Symphony of the Night.
There is very little information on Bloodletting's story. All that is known is that it would have featured Richter Belmont and Maria Renard as the protagonists, and that there was some sort of rival-antagonist whose goal may have been outperforming Richter in some way.
The only image proof that The Bloodletting ever existed are sprites of Richter and Maria donning slick, modern-looking outfits, and the antagonist. It also seems that these sprites may have been recycled for Symphony of the Night, namely Richter's sprite looks very similar to that of Fake Trevor's from the inverted Colosseum boss fight.