While you can reach Bloodstained: Ritual of the Night‘s bad ending fairly quickly, seeing the good ending requires considerably more work.
As soon as you gain access to the Hall of Termination area, you can defeat Gebel and bring the game to a close. But you don’t want to finish Bloodstained: Ritual of the Night on a bad note, do you?
To view Bloodstained: Ritual of the Night‘s true ending, you need to wait to fight Gebel until you’re fully prepared. Basically, you need Zangetsu’s sword, which is capable of slashing the moon in the background during the fight when it turns red. But to get Zangetsu’s sword you’ve got a lot of additional adventuring ahead of you.
Your aim is to reach the Oriental Sorcery Lab which lies beyond the Dian Cecht Cathedral, but to get there you need to be able to walk through spikes. On your way to doing that you’ll need to gain the ability to breathe underwater and invert gravity. Once you are able to get through the hallway full of spikes, however, explore what lies beyond until you reach the Oriental Sorcery Lab.
In the Oriental Science Lab, you’ll eventually find Zangetsu and fight him for a second time. When you beat him he’ll give you his sword which is pretty powerful. Even more important, however, is the fact that it can slice moons in two.
With the sword in your possession, head back to the Hall of Termination and head off to fight Gebel. While fighting him, though, keep an eye on the moon in the upper right hand corner of the screen. As soon as it turns red, jump up and slice it in two with Zangetsu’s sword. Ta da! It turns out Gebel was being controlled all along!
To continue the game and view the true ending, all you then need to do is head back to the Garden of Silence. If you recall, when you first started playing the game, just before fighting Zangetsu for the first time, there was an outdoor area where there was a bright red moon. Head there and slash the moon with Zangetsu’s sword. You’ll then be able to warp to the Den of Behemoths. Simply carry on from there, and you’ll be able to view Bloodstained: Ritual of the Night‘s true ending.