Here is the full list of all 29 River City Girls achievements. It takes around 10-12 hours to unlock all of the achievements on Windows.
Completed the game with a secret character.
Destroyed all Sabu statues.
Reached Max Level.
Catch a dodgeball thrown by your ally.
Parry 10 enemy attacks.
Complete the game in Co-Op.
Completed the game on Hard.
Reach 100% completion.
Completed all of Godai's quests.
Catch a boomerang.
K.O. the secret boss.
Was defeated in detention.
That wasn't very nice!
Enter the Mall.
Obtain an item from the Pawn Shop.
Find the keys in the junk yard.
Enter the Penthouse.
Collected $5000
Defeated an enemy with a fish.
Defeated an enemy by hitting them with another enemy.
K.O. Yamada.
K.O. Hibari.
K.O. Abobo.
K.O. Noize.
K.O. Sabuko.
Destroy a vending machine.
Equip a new outfit.
K.O. Misuzu.
Attacked Mr. Rudis.