Here's an Achievement Walkthrough with commentary showing both endings for those who prefer video guides. You should be able to follow along by just listening to my voice since I tell you which choices to make.
Timestamps:
Prologue / Human Ending Playthrough 0:43
Luccretia Ending Playthrough 10:05
Secret Discussion 19:35
Options to change before starting
Text Speed - Max
Auto-Play Speed - Max
Skip Mode - All
Stop skipping after choices - No