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