Here is the full list of all 26 Eternights achievements.
Earned all trophies.
Going out with 1 person only til the end.
You scavenged 10 city items.
Reach max rank with all your confidants.
You went on all of Yuna's dates.
You went on all of Yohan's dates.
You went on all of Min's dates.
You went on all of Sia's dates.
Date every dateable character.
Reached max rank with yourself.
Reach max rank with a Confidant.
You went on all of Chani's dates.
You made a promise with Yohan.
You are a social butterfly.
You made a promise with Min.
You made a promise with Sia.
You made a promise with Yuna.
You retrieved the Stone.
You helped Min break through the second wall.
Now you know how to give proper piggyback rides.
You helped Yuna destroy the first wall.
You got creative with your hand.
You explored the city for the first time.
The start of a peculiar bond.
Escaped the shelter.
You awakened your new arm.