Here is the full list of all 17 Umihara Kawase Shun Steam Edition achievements.
Finish all doors
Visit all stages
Obtain all backpacks
Catch all enemies
Travel upwards 2 screens or more without touching the floor
Finish "UmiharaKawase Shun" without losing a life
Finish Pufferfish battle with only blowing it away twice
Let 3 birds land on body at the same time
Finish Stage 0 within 10 seconds
Finish Stage 0 within 15 seconds
Use door that returns to Stage 0
Catch 3 Flying Fish that jumps from the bucket
Make a catch after moving more than 2 screens with lure attached to the enemy
Catch Sharksucker thrown by Shark while in air
Catch all Squids during Squid battle
Finish "UmiharaKawase Shun"
Catch all Kid Frogs during Tadpole battle