Uh-oh

[Tavrobel]

Pain does not cause Death 100% of the time. It causes it approximately 95% of the time. If you don't get hit by Death, you will most assuredly get hit by everything else (or die from the sheer amount of damage). Deathproof would help, if the challenge were valid at all. In the Via Purifico, Tidus is not one of the characters found in Yuna's challenge, so therefore, the challenge is flawed in its design, at best.

It's not impossible (just overlevel alot), but fundamentally rule breaking. Also, you characters revive after every fight with one HP. Have fun killing them and always missing! Additionally, the Yuna section in the Via Purifico will kill you because you did not level her at all (nor are you allowed to use her). If the Fiends don't get you (and the encounter rate is lowered immensely inside), Isaaru will.

Anima during Seymour's first duel has 18000 HP.

Deathproof requires sixty Farplane Winds, which can be bribed from Ahriman (a fiend inside of Sin and the Omega Ruins), 56k for an average of six. Bribing Wraiths also give Winds, 444,440 for sixty of them (another Sin/Ruins fiend). Alternatively, you can go for Deathward, which requires fifteen Farplane Shadows, which can be stolen from Master Coeurls. Wraiths offer Shadows as steals, and several Cavern of the Stolen Fayth enemies offer Shadows for a steal as well.

What I'm trying to say, is that there's absolutely no way you can get Deathward or Deathproof before Anima. None of the equipment sold by shops (including O'aka's) will sell Death equipment.