Here is the full list of all 56 An Oath to the Stars achievements.
Defeat Seikatsu on any difficulty
Defeat Kanashimi on any difficulty
Defeat Ghimonten on any difficulty
Defeat Nintai on any difficulty
Defeat Chiyoko on any difficulty
Clear Stage 1 on Normal or higher difficulty with a A rank
Clear Stage 2 on Normal or higher difficulty with a A rank
Clear Stage 3 on Normal or higher difficulty with a A rank
Clear Stage 4 on Normal or higher difficulty with a A rank
Clear Stage 5 on Normal or higher difficulty with a A rank
Clear Stage 1 on Normal or higher difficulty with a S rank
Clear Stage 2 on Normal or higher difficulty with a S rank
Clear Stage 3 on Normal or higher difficulty with a S rank
Clear Stage 4 on Normal or higher difficulty with a S rank
Clear Stage 5 on Normal or higher difficulty with a S rank
Clear Stage 1 on Hard or higher difficulty
Clear Stage 2 on Hard or higher difficulty
Clear Stage 3 on Hard or higher difficulty
Clear Stage 4 on Hard or higher difficulty
Clear Stage 5 on Hard or higher difficulty
Clear Stage 1 on Hard or higher difficulty with a A rank
Clear Stage 2 on Hard or higher difficulty with a A rank
Clear Stage 3 on Hard or higher difficulty with a A rank
Clear Stage 4 on Hard or higher difficulty with a A rank
Clear Stage 5 on Hard or higher difficulty with a A rank
Clear Stage 1 on Hard or higher difficulty with a S rank
Clear Stage 2 on Hard or higher difficulty with a S rank
Clear Stage 3 on Hard or higher difficulty with a S rank
Clear Stage 4 on Hard or higher difficulty with a S rank
Clear Stage 5 on Hard or higher difficulty with a S rank
Clear Stage 1 on Inferno difficulty
Clear Stage 2 on Inferno difficulty
Clear Stage 3 on Inferno difficulty
Clear Stage 4 on Inferno difficulty
Clear Stage 5 on Inferno difficulty
Clear Stage 1 on Inferno difficulty with a A rank
Clear Stage 2 on Inferno difficulty with a A rank
Clear Stage 3 on Inferno difficulty with a A rank
Clear Stage 4 on Inferno difficulty with a A rank
Clear Stage 5 on Inferno difficulty with a A rank
Clear Stage 1 on Inferno difficulty with a S rank
Clear Stage 2 on Inferno difficulty with a S rank
Clear Stage 3 on Inferno difficulty with a S rank
Clear Stage 4 on Inferno difficulty with a S rank
Clear Stage 5 on Inferno difficulty with a S rank
Clear Stage 1 without being hit on Normal or higher difficulty
Clear Stage 2 without being hit on Normal or higher difficulty
Clear Stage 3 without being hit on Normal or higher difficulty
Clear Stage 4 without being hit on Normal or higher difficulty
Clear Stage 5 without being hit on Normal or higher difficulty
Clear all stages in a single run
Clear all stages in a single run on Hard or higher difficulty
Clear all stages in a single run on Inferno difficulty
Clear all stages in a single run on a single credit
Clear all stages in a single run on a single credit on Hard or higher difficulty
Clear all stages in a single run on a single credit on Inferno difficulty