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.
Both girls ending
Every ending achieved
Special scene with Reika!
Arisa ending
You finished the game super fast!
Kaguya ending
You saw one of Kaguya's gorgeous appearances in a dress!
You defeated the enemy!
You defeated the enemies!
You played the Japanese version of the game
You played the game in both languages
Are you ready to experience Sakura Nova?
You played the English version of the game