Here is the full list of all 15 I Think I'm in Love with a Demon Prince achievements.
Complete your first battle.
Complete the game.
Earn a 3 star rating on Yurei Castle.
Earn a 3 star rating on Valley Road.
Earn a 3 star rating on Mountain Road.
Earn a 3 star rating on Snake River.
Earn a 3 star rating on Maple Forest.
Earn a 3 star rating on Forsaken Mines.
Earn a 3 star rating on Farming Village.
Earn a 3 star rating on Ancient Ruins.
Earn a 3 star rating on Bleeding Volcano.
Earn a 3 star rating on Poison Swamp.
Earn a 3 star rating on Shipwreck Croft.
Earn a 3 star rating on Jomon Castle.
Earn a 3 star rating on all levels.