Here is the full list of all 39 Swords Souls: Neverseen achievements. It takes around 20-25 hours to unlock all of the achievements on Windows.
Complete endless stage 120
Complete endless stage 100
Complete the museum to 100%
Complete endless stage 80
Get all Soul Master medals in all training areas
Complete endless stage 60
Complete endless stage 40
Become friends with all mercenaries
Become friends with two mercenaries
Become friends with a mercenary
Complete endless stage 20
Catch 8 different types of fish
Catch 11 different types of fish
Beat the final boss using only beginner armor and weapons
Find all lost children
Tame all pets
Tame 8 pets
Defeat chapter 6 boss
Defeat chapter 5 boss
Become Soul Master in all training areas
Get three Combo medals of rank Soul Master
Get three Combo medals of rank Platinum
Defeat chapter 4 boss
Defeat the Legendary Hunters
Juggle with the same coin 30 times
Get three Combo medals of rank Gold
Defeat chapter 3 boss
Juggle with the same coin 20 times
Juggle with the same coin 10 times
Get 3 perfect in a row while fishing
Trigger the Oof ring once
Defeat chapter 2 boss
Get three Combo medals of rank Silver
Tame 3 pets
Catch 3 different types of fish
Defeat chapter 1 boss
Get three Combo medals of rank Bronze
Defeat the Mama Mole
Get three Combo medals of rank Wood