Here is the full list of all 15 Sakura Nova achievements. It takes around 0-1 hour to unlock all of the achievements on Windows.
Arisa ending
Every ending achieved
Kaguya ending
You saw one of Kaguya's gorgeous appearances in a dress!
You played the English version of the game
You played the game in both languages
You played the Japanese version of the game
Both girls ending
You finished the game super fast!
Special scene with Reika!
You defeated the enemy!
You defeated the enemies!
Are you ready to experience Sakura Nova?