Here is the full list of all 29 Yggdra Union achievements.
Clear Chapter 1
Durant joined the team
Flunky get MVP
Nietzsche joined the team
Rosary joined the team
Roswell joined the team
Mistel joined the team
Russell joined the team
Cruz joined the team
Pamela joined the team
Elena joined the team
Clear Chapter 2
Clear Chapter 3
Clear Chapter 4
Clear Chapter 5
Clear Chapter 6
Clear Chapter 7
Clear Chapter 8
Yggdra class changes to La Pucelle
Exceed 10% item completion rate
Exceed 30% item completion rate
Exceed 50% item completion rate
Exceed 80% item completion rate
Complete all items
Get all Cards
Clear HARD difficulty
Clear Ending A
Clear Ending C
Clear Ending D