I'm currently fighting him as terra in critical mode.

 

I'm level 48 and i cant seem to get him past 2 bars

 

I had to level up to level 65 in order to beat him. This is what your deck should look like, thunder surge x4, Arieal Slam x2, Curaga x2. Then have ultimata cannon as shotlock. Good luck!

I can not be defeated.

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use cura

You know, the first time I fought No Heart, I was frickin scared, but as I fought him, I found that the battle wasn't as menacing as I thought it would be!  You see, the key to this battle is keeping a close eye on his movements and just dodge like hell!  You also have to keep in mind that No Heart leaves himself pretty open to attack, so you should capitalize on that by having a few Mine Squares in your deck, because Mine Square helps, believe me!  And so, if you have the Rhythm Mixer command style, use it, because it's also a huge help, especially when doing the Rhythm Mixer attack in general.  Using Ultima Cannon is also an effective strategy, since it can chip away at his health considerably.  But yeah, be at least at level 60 to fight No Heart, or, if you don't want to level grind, just simply learn his strategy, because he has a predictable moveset.  What makes the battle so irritating is the fact that the motherlover is frickin fast!  His speed is his true strength!  And with these words of friendly advice, I say to you, good luck!