Which quest unlocks Inferlupa's evolution?

The Warrior is time-gated and takes about two real-world days, so start it early. You can't rush it. Plan for the wait and do something else in the meantime.

Finishing the quest does not evolve anything by itself. It only unlocks the evolution. You still have to spend six Unbroken Flameruff Spirits on it, and Flux Crystals can't stand in for them.

The quest is also useful outside this evolution. The Beast Fang Ridge leg of the Fragrant Journey needs the Flareburst Flower, and that flower requires The Warrior. One quest clears both.

Farming the six Unbroken Flameruff Spirits

The spirits come from one place: Flameruff the Mighty. It is a special elite Gamma-stage Flameruff that appears in the daytime in the Inferlupa elite battle area. You have to defeat it. Capturing it gives you no spirit, and an ordinary Flameruff without the title never drops one.

Even a win is not guaranteed. The spirit is a low-chance drop that comes in place of an evolution stone, so expect to fight it several times to collect six. If you lose track of what is still missing, select 'how to get' on the requirement in the evolution menu. It shows which Aniimo drops the material and how to obtain it.