This game is around 40 minutes to an hour long. I suspect with this guide, even 20 minutes will be possible. I will detail every ending, even the final achievement which is a little misleading to get.
All Endings + Achievements
Treat her well the entire way, during the end dialogue (Day 4), intervene and there will be third option. Select that
Ending 2: The Same Stars
Complete the same steps as ending 1, however select the top option this time instead of the third option (I believe the second option also works)
Ending 3: Routine
Treat her normally, neither kind or cold, intervene on Day 4 and select the top option.
Ending 4: A Forgotten Star
Treat her normally, neither kind or cold. On Day 4, do not intervene. Let the guards take her away.
Ending 5: Condemnation
Treat her normally, neither kind or cold, on Day 4 intervene and select the bottom option “Why did you commit arson?”
Ending 6: Hasty
Day 1, kill her instantly (I believe any time during Day 1 also works)
Hidden Ending: Coward
Day 1, when she tells you to press the button, do it
Ending 7: Regret
Day 2, kill her
Hidden Ending: Mercy
Day 2, give her bread. Wait for her to say “Thank you…” Kill her immediately while the text is still up. (Muahaha!)
Ending 8: Self-righteous
Day 3, kill her
Ending 9: Alienation
Treat her well the entire way until Day 4, intervene, pick the third option. When she confesses her innocence to you. Kill her immediately. Do not let it pass on to Day 5. (Her legacy shall be that of a terrorist muahahaha!)
Ending 10: Grudge
Treat her normally till Day 4, intervene, select the top option. She proves her innocence. Pass on to Day 5. Kill her immediately (muahahaha! She really thought she was going to live!!!)
Ending 11: A Falling Star’s Goodbye
Treat her well the entire way, during the end dialogue (Day 4), do not intervene. Let the guards take her away.
Ending 12: You’re No Dragon
Day 2, enquire about whether her horns can be broken, break her horns (works the next day). Day 4, kill her instantly before she can speak.
5omeday (Watch all Endings)
Complete Ending 1 again to get this achievement after completing all endings.
If you made it this far, wrote which ending you got first! For me it was Hasty, then Grudge. I just couldn’t resist myself ahahah!