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