Here is the full list of all 69 Angel Wings achievements.
Unlock all Chaeng outfits
Unlock Chaeng's Medium Ending
Give Chaeng the phone
Watch drama together
Enter the drum studio
Unlock Nuri's Good Ending
Fight!
Control your emotions
Go skating
Party time!
Eat ramen with Yujeong
Meet Nuri
Select the World card
Complete any route
Unlock all Seola outfits
Unlock Seola's Medium Ending
Defeat Kaori
Play video games together
Win a basketball game
Follow Jihyun
Eat chicken together
Complete the lake run
Stick around for extra practice
Complete an activity with Seola
Leave class early
Select the Hierophant card
Begin a Route Selection campaign
Complete the game once
Unlock Jei's Medium Ending
Tell Jei the truth
Help out with cooking
Attend the work party
Go to the forest together
Attend the beach
Buy some food
Take a coffee break
Eat salad together
Choose stealth mode
Go to the mall with Chaeng
Visit the phone shop
Complete the work assignment
Enter the bar
Complete an activity with Yujeong
Select the Hermit card
Pick up the phone
Check the computer
Unlock Kei's ending
Unlock all Kei outfits
Unlock Chaeng's Good Ending
Jump into the hotel pool
Unlock Hyedong's Medium Ending
Unlock Hyedong's Good Ending
Unlock all Hyedong outfits
Unlock Jei's Good Ending
Unlock all Jei outfits
Unlock Nuri's Medium Ending
Choose to help Yujeong
Receive the sheet music
Unlock all Yujeong outfits
Unlock all outfits
Complete all routes
Reject the current timeline
Unlock all Nuri outfits
Unlock Seola's Good Ending
Unlock Yujeong's Medium Ending
Unlock Yujeong's Good Ending
Complete the band
Unlock Yuri's Ending
Unlock the true ending