Here is the full list of all 49 Nights of Azure achievements.
Viewed an ending.
Defeated Ludegert.
Collected 50% of items.
Defeated Corrine.
Summoned a Servan 100 times.
Executed a trade for the first time.
Defeated Blueblood Dragon Mavelus.
Defeated Blueblood Maiden Milaya.
Collected 50% of Servans.
Defeated 1,000 enemies.
Defeated Blueblood Count Rosier.
Transformed into Demon form.
Defeated Blueblood Cavalry Carousel.
Achieved 100-Chain.
Cleared first Arena task.
Completed first task.
Defeated Blueblood Dragon.
Actualized a Servan for the first time.
Defeated 100 enemies.
Gave an order to a Servan for the first time.
Summoned a Servan for the first time.
Collected all achievements.
Defeated Mistral.
Defeated Christophorus.
Viewed an extra ending.
Summoned Servans 1000 times.
Gave 100 orders to Servans.
Gave 1000 orders to Servans.
Actualized 40 Servans.
Actualized 80 Servans.
Executed trades in half of the world.
Executed trades all over the world.
Completed 100 tasks.
Completed 300 tasks.
Cleared half of Arena tasks.
Cleared all Arena tasks.
Collected all Servans.
Collected all items.
Achieved 300-Chain.
Achieved 500-Chain.
Defeated 10,000 enemies.
Transformed into Rabbit form.
Transformed into Phantom form.
Transformed into Armor form.
Transformed into Nightmare form.
Arnice equipped Hamelin's Pipe and cleared a battle.
Arnice equipped Glass Blade and cleared a battle.
Maxed out a Servan's level.
Arnice achieved her max level.