Here is the full list of all 15 Flowers of Satsunai achievements.
Unlock all Nanami's romance scenes
Unlock all Yui's romance scenes
Unlock all Kyoko's romance scenes
Unlock all Akane's romance scenes
Unlock the best ending
Reach the 6th challenge in Survival mode
Reach the 11th challenge in Survival mode
Reach the 21st challenge in Survival mode
Rank SS in one survival game
Use 5 spells in one game
Use 10 spells in one game
Create a 'chain + 4' in one game
Create a 'chain + 8' in one game
Create a 'chain + 12' in one game
Click on the fox-spirit maidens 15 times during one game