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