To unlock the best, good or true ending of Bloodstained: Ritual of the Night (ROTN) you’ll have to complete certain tasks. The first thing you must do is to get to the Oriental Sorcery Lab, for that you’ll also need some special powers.
To get to this place, you have to go to the first room of the castle, and at the top you’ll find a corridor full of spikes and if you want to pass that you’ll need three fragments, with that you can access this new area.
- Craftwork: You can get this by defeating the boss in the Cathedral of Dian Cecht.
- Invert: You can succeed by defeating the head of the Inferno Cave.
- Aegis plate (Spike Immunity): You can get this in a chest of the Twin Towers Dragon.
Once you reach there you’ll have to defeat all the enemies including Zangetstsuto, defeating him will get you his special sword. This one is essential to get to the end of the game.
Once you get this blade you’ll already get the secret ending, what you have to do is use this weapon to defeat Gebel, the final boss. Once you have defeated him, a moon will appear, you’ll have to attack it and it will turn red until you cut it. Then the final secret boss of the game, Gremory, will appear and you'll have to look for it in another area of the map.
To find Gremory you must go to the Garden of Silence and enter the red corridor that is over the carriage. Once there you must cut the red moon and that will take you to a new area, where you’ll find Alfred and Zangetstsuto, and if you get to the end you’ll find Gremory, kill him to get to the good end.