Here is the full list of all 20 Kare wa Kanojo achievements.
Complete the first chapter
Complete the second chapter
Complete the third chapter
Complete the fourth chapter
Complete the fifth chapter
Finish the game for the first time
Get a kiss from Sakura
Get a kiss from Rika
Get a kiss from Nanami
Find the truth about Sakura
Tell Sakura the truth about the yukata
Choose to game at the beginning of the game.
Help Rika with the festival
Grope Rika (accidentally)
Prank your friends with Nanami
Help Sakura tell the truth to Nanami
Complete Sakura's route
Complete Rika's route
Complete Nanami's route
Find the secret code in the game