Godlike
Persephone (Wild ARMs 5) vs Sora (Kingdom Hearts Series) - This is much closer than most people give it credit for. First, this only applies if you vote on KH1 Sora. I haven't done the math for KH2 Sora. Second, note that because of Second Wind/Chance, Sora can only be killed if Persephone can 'triple turn' him. That is, she needs a turn to prep Gatling Gun, a turn for Gatling Gun and a follow up turn to kill Sora. Assuming Sora is average and using NEB's data on Persephone, we get the following:
Persephone on base - 125% average
Persephone after Quicken - 147% average
Persephone - Cast Quicken (80th Clocktick)
Sora - Ars Arcanum (100th Clocktick)
Persephone - Targetting: ON (134th Clocktick)
Persephone - Gatling Gun (168th Clocktick)
Sora - Curaga (200th Clocktick)
Persephone - Targetting: ON (236th Clocktick)
Persephone - Gatling Gun (276th Clocktick)
Sora - Curaga (300th Clocktick)
Persephone - Targetting: ON (338th Clocktick)
Persephone - Gatling Gun (372th Clocktick)
Sora - Curaga (400th Clocktick)
And so on. Sora's only chance is to kill Persephone first, which he has a good argument for. Ars Arcanum deals 2.69x average, so if you see Persephone as only about 2 PCHP, he will 2HKO first. Otherwise, Persephone wins through heal locking. Even though Sora can stay afloat with Curaga forever (MP Rage ensures he will never run out of MP), he won't get a chance to do Curaga -> Ars Arcanum safely because he is naturally slower.