Dragon Ball: Raging Blast

This can be done easily, even if you are a newcomer to the game, it may be hard to begin with, but playing through the game once on easy or normal you will get to grips with the controls and how each character operates.
Most of the characters have the same button combinations to do the same combos, if you get stuck doing this just try to either keep your distance and fire super attacks or ultimates, or you can go in close and spam your desired combo.
Make sure to take your time too if you aren't too great at the game.

I suggest doing this achievement after beating each battle on Easy/Normal. Not only will this help you understand each mission better (and where the story segments might screw you up), but it will also unlock the missions for each stage, one of which is always "Beat on Hard". This will also help you get the "Star Holder" achievement, as you'll unlock a star for each battle you beat on Hard if you wait until you've completed it once already.

The thing that throws everyone off is the association of "Hard" with "I can't beat that mode cause I'm not good enough". Well, Hard in Raging Blast is pretty easy if you've gone through the tutorials and spam super attacks. Trust me, if I can get it, so can you.

The easiest way I've found to win most of the time is to perfect Snap Vanishing (tapping RB as an opponent attacks you) and to spam Smash Attack 4 (XXXXY) and use a KI based Super Attack while they're stunned (usually Up on the Right Stick). You can also use Air Combos (Smash them up into the air with either holding Up + X or X, Up+Y then AXXXXX) and Pursuit Attack 2 (X after sending your opponent flying) to gain KI and attack. Another thing that's almost unfair is to spam rush moves, such as Goku's Meteor Combination or Trunks Save the Future, as 9 times out of 10 the computer will not respond quick enough to stop it (the other time it will guard cancel the computer).

If you're running low on health, make the computer come to you by using a Super Rising (LT + LB), which will send you to the top of the map. From here, you can charge your KI up. You can either use a Smash Attack Low (X, Down + Y) to send them falling to the ground or fire off a Super when you know they're coming up, trapping them in an unblockable Super Attack.

If the computer counters you or sends you flying, that's the best time to use Snap Vanishing, as they're pretty predictable with their pursuit attacks. Watch your opponent carefully and the moment the computer is about to hit you, tap RB and you'll teleport behind them. You can press X to send THEM flying instead. Once you get the timing down, you'll know practically everything you need to.

As Jenova20 stated, make sure you purchase all the battles from the shop. You can use the stars you get from beating the missions on hard to unlock the new stages (if you haven't already done so). While most sagas only have one battle missing (some require you to purchase the first and beat it to unlock the next), the What If Saga contains way more and should be saved for last.

Good luck and I hope my tips helped you learn how to tackle Hard mode. If you followed my advice, you'll also unlock the following achievements: