You can't miss these achievements if you finish the game.

A Real Worrkout
Beat Misuzu


Shop until they drop?
Enter the Mall


Defeating the Dark Arts
Beat Yamada


Bona fide bargain
Obtain the golden cat from the Pawn Shop


Fashionable Beatdown
Beat Hibari


Master of Unlocking
Find the keys in the junk yard


A Bye Bye
Beat Abobo


So Metal
Beat Noize


An Explosive Entrance
Enter the final boss area


Like Father Like Daughter
Beat Sabuko

Your Lessons are Boring!
Attack the teacher in detention area you start in the game


This is technically missable but you will most likely try to hit someone near him and get it by accident

Killed by Math
Was defeated in detention


Die in the first room of the game, start the game let the enemy spawns then go get a drink and hit continue when you get back to move on to the rest of the game.

Full Service
Destroy a vending machine


I would be surprise if you didn't get this naturally, but just destroy a vending machine.

Stylish
Equip a new outfit


Just equip an accessory and you got the achievement, if you somehow beat the game without getting this achievement that is impressive.

Friendly Beatdown
Defeated an enemy by hitting them with another enemy.


At level 6 you should unlock human weapon, this allows you to pick up enemies that are laying down and use them as a weapon for a brief period of time. Just use one to KO an enemy and the achievement is yours.

Back at me!
Catch a boomerang


You can find a boomerang around the third area either in the toy section or the bridge to the third boss, throw the boomerang and parry it when it comes back and you will catch it.

Carpe diem
Defeated an enemy with a fish


You can find a giant fish in the fifth area on the beach, pick it up and KO an enemy and bingo you get the achievement

Help an Old Pal?
Completed all of Godai's quests


There are 5 missions one in every level after the school, after first one keep an eye out for dumpsters and go near it and Godai will pop up and give you a mission finish it. Then as you go to the next zone find him again and rinse and repeat.

River City Ransom
Collect $5000


Pretty self explanatory, but key point you don't need to have it at the same time. You just need to have had a sum amount of 5000 collected. You might not get it in the first playthrough but pretty sure I did so putting it here. But if not, go into loitering mode which is free roam mode and beat the secret boss and you should have enough money.

Smashed Statues
Destroyed all the Sabu statues


There are 25 statues spread through out the game destroy all 25 to get the achievement and an item. Which is one of two items necessary to unlock the secret boss in the free roam mode.

Credit to Shadiochao for the video location guide










Perfect Parry
Parry 10 enemy attacks


This one can be a bit weird I got it by having 10 parries in one play session, I essentially just went to the courtyard with the volleyballs after you clear the screen lock there, went out and went back in and KOed 2 of the 3 enemies that will spawn there and parrying 10 times on the remaining enemy. That should get you the achievement.

O.M.G Seriously?
K.O. the Secret Boss


After beating the game you will gain half a heart with a red K, and if you broke all the Sabu Statues you will get the other half of that heart with a blue M. Now go into free roam mode and put both into your accessory slots and enter the final boss room. This will spawn the secret boss. Beat them and you get the achievement and a big in game reward of experience and cash.

TAKE THE WORLD ON
Completed the game on Hard.


You only need to beat the final boss on Hard, you can either play the game on hard or leave before the final boss and set it to hard then fight the boss. Either way you will get the achievement.

A New Challenger
Complete the game with a secret character


You will unlock 2 secret characters after you beat the game the first time, either grind one of them up in new game+ or have them as your second character that you put them into a corner and beat the final boss in the free roam mode and you get the achievement.

Don't mess with us!
Compete the game in Co-op.


Similar to A New Challenger, you only need to beat the final boss in Co-op either plug a second controller and put the character in the corner as you fight the final boss. Can be doen either in the first playthrough or in the free roam mode. You can also do it naturally as it a fun game with a friend but its up to you.

Power Up
Reached Max Level


Max level is 30, you should be at around the low 20's when you beat the game and you should get enough experience beating the final and secret boss a few time for the previous achievements and going through the New Game+ with you highest level character that you should reach the max level.

Renegade
That wasn't very nice


To get this activate friendly damage in the setup so you can damage you co-op partner, KO your partner and you got the achievement. You can do this in actual co-op or just plug in a second controller. Either way works.

You're out!
Catch a dodgeball thrown by your ally


Similar to the boomerang achievement, you do need a second controller or co-op partner but have them throw a dodgeball/volleyball that you can first find in the area to the left as you leave the school and parry the ball before it hits you and you will catch it.

Completionist!
Reach 100% Completion


To reach 100% on a file you need to for sure do the following:

• Beat the game
  
• Finish all side quest
  
• Unlock all moves for all 4 playable characters
  
• Eat every food item
  
• Buy every accessory

I have yet to confirm whether or not you need to:

• Destroy all Sabu Statues

Was confirmed by another player that you don't need to beat the Secret Boss or get all the cats in New Game+ to get the Completionist achievement but I will leave the guide here just in case you want to do it while you do New Game+. As it rewards you an accessory that will give you infinite SP.

Once again credit to Shadiochao Cat location guide