OMORI

To get the good ending, you must be on True Route and check what Basil is doing. You'll engage in a fight, and after that, you have to fight Omori. It's impossible to defeat him the first time, so you'll lose (However, if you die too early, you'll get a simple Game Over, so fight him until "Omori did not succumb" turns to "Omori will not succumb). Press Yes when the game gives you an option to continue. After that, you get a very emotional scene with Duet playing. After waking up, go where Stranger is going instead of your Dream World friends, and tell your friends the truth.

Bonus: if you watered Basil's flowers (which you should anyway) during Three, Two and One Day Left, you get the secret ending between Sunny and Basil.

Enjoy the credits and congratulations on beating an amazing game!