Mr. Tines: Seventh degree burns, and she can still hold it!
Reichu: I had never even heard of anything beyond third degree burns. Apparently "seventh degree burns" don't even exist, but they do go up to six:
Burns of the fourth degree, which follow the prolonged application of any form of intense heat, involve the total destruction of the true skin… In burns of the fifth degree the underlying muscles are more or less destroyed, and in those of the sixth the bones are also charred.(Source)
Since they only mention "damage to the epithelium" in C-263 — and judging by here hand here, that's what it looks like — they seem to be employing a burn-severity system different from what we're used to. Either that, or they're just pulling the numbers from thin air.