Dracula X: Rondo Of Blood: Play as Maria
When the minotaur chases Richter in Stage 2, get the Key subweapon from the candlestick. Go down into the sewers after the minotaur gets blocked by the wall. Use the Key subweapon on the locked door at end of the sewer. This will trigger an intermission sequence showing Maria joining Richter. She can now be selected as a playable character at the main menu.