To evaluate the extensive hax that both sides have at their disposals...
Okay, Bartz's AP and Durability are at a huge disadvantage, so he could get oneshotted. However,
Resurrection, using Haste to speed himself up, and the use of Attack Reflection reflecting most of her hax with Wall, and using Barriers and
Teleportation to evade, he should be able to outlast her pretty well. This would give him enough time to learn her resistances and his
Precognition that can see nearly a minute in the future if I recall correctly would be to his aid even further to evading her attacks. The effects of her Pocket Reality seem like they would only be useful to slow him down(assuming it does that), as the other stats I have already regarded as irrelevant. While Bartz doesn't have it on his page, he is capable of attacking and affecting
intangible beings with his attacks, so her Intangibility won't help here. The
Invisibility wouldn't be of much use because he would already know where she would be attacking because Precognition. Bartz should also have Immortality Type 7 because of the Necromancer class making him become undead, so I don't really think eating his soul would be of too much of a hindrance, though I'm not entirely sure how it works. While Nero resists a lot of the hax that Bartz can perform, he can still
send her to the Void,
age her till she's old and crippled,
turn her into a Toad,
make her extremely small,
drain her life force,
put her to sleep, paralyse her, and
poison her, and if her soul-eating would fail to work, as in, he dodges or his Type 7
Immortality actually prevents it from fully working, he could
copy the attack, likely the same thing with her Pocket Reality, too. Her Resurrection is also limited, so there's that.
I think you get the point I'm trying to make. My vote goes to Bartz.