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