Here is the full list of all 9 Demon Slayer Akagi achievements.
Get a Score gold star on every practice stage
Get a Time gold star on every practice stage
Clear every boss with a gold star
Clear the game on Normal mode without a game over
Clear the game on Hard mode without a game over
Clear the game on Lunatic mode without a game over
Obtain a gold star on all challenges
Clear the game
Clear any challenge or practice level with a gold star