Well, I saw the walkthrough the dev made, and It's really filled with flags at the end that if you don't give it a lot of tries to the game by yourself you won't notice, I have already had my fill with this game, and got tired, I tried killing the red succubus and sparing her, reaching with little to almost no sinful bar the end and I couldn't trigger the true ending, if someone did, I'm happy for you, but I couldn't, and the game should have clear pointers if you're wanting to reach a "good ending", at least to my understanding...