How do you get a perfect Pawney?

The timing is the whole trick: once you pull the sword in that quest, this route is gone. So the order matters. Catch a Helmut that is already perfect, keep it with you through The Legend of Helmuts and Helgons, and evolve it while the quest is still running. Do that and the Pawney you get is perfect, with no rolling and no upgrade grind on top.

If you pull the sword first, or bring a Helmut that is not perfect, you lose the guarantee. You can still raise a lesser Pawney later, but an Elite one sits a full tier below Perfect and has to be pushed up with upgrade resources. A perfect starting point costs you nothing further, which is why this quest window is the cheap way to do it.

Perfect-quality Aniimo can also come out of eggs, Prismana eggs included, but that is a matter of luck. The quest route is the only one here that is certain.

Why Pawney is worth getting perfect

Pawney has the highest attack of the six free Prismana Aniimo offered at Junior Wayfarer rank. It also brings Hookshot, a mobility skill that aims at the centre of your view, stretches Pawney's arm and pulls it to whatever it hits, wall or enemy. That makes it useful both for getting around and for closing on targets in a fight.

Not settled: Pawney's exact base attack is not settled: it is given as both 128 and 125, though it leads the six free Junior Wayfarer Prismana Aniimo either way.