Oh boy, Zelkova isn't going to like that one.
I assume this is when we attempt to seal those flames with ofuda only to have them burn afterwards because the material isn't resistant enough.
We could initially test out how the flames react to our corrupted water and earth ofuda. Although I doubt Shinji's decay is enough to starve the flames, the element themselves might allow to open a path, even if only temporarily.
Outside of the various factors that could be dangerous (heat, monsters, traps and such), I think the main issue is to find a way through. Not only the labyrinth is constantly changing, it will probably provide stuff that will cause disorientation. So, even if we have the means to ditch it out against whatever is inside (like Fusion), we will need a sure way to navigate through.
Too bad we didn't study runes harder, for we could have used Berkano here.