Here is the full list of all 22 Piko Piko achievements.
Finish the game.
Knock the Hammer Cat's hammer back at em!z
Get in the Neon Fusion blaster
Get to Level 10
Defeat Fruggles
Defeat a Bomb Cat with their own Bomb.
Defeat π-ko
"Attempt" to rescue the balloon.
Swoooooooosh!
I don't think this is the School path...
Defeat Tanker Girl
Join up with your floof fox friend Nyan!
Run or you're gonna be late!
Beat Cookiebius
Get to Level 20
Get to Level 50
Help the Bike Girl
Mess up Nyan's house
Get in the school without Nyan in your team.
Defeat the hidden witch boss
Get 999g