「燃えてなんぼの!!!」「"黒炭"に候っ!!!」
Okay... this is some weird old Samurai speech or something (yeah Wano...), so I don't perfectly understand it. Honestly a bit above my cultural literacy.
"Burning" and the name "Kurosumi" (which means Black Coal) fine enough, but the use of Nanbono here is hard to interpret when I never hear it in a contemporary context, but it's like "how much" or "how many", but could also be "No matter how much". Here, like in many Japanese (especially old Japanese) sentences many grammar indicators are dropped (is, am, are, then, etc.) because you're expected to understand. So taking the leap, "No matter how much [pronoun] burns", here pronoun is not included so it could be "it" or "they" or "you"-- the subject isn't made clear, but essentially it's "Kurosumi" but again is that this man specifically or the clan in general or both?
And then "Sourou" here is super confusing because it's meaning is super hard to define. The sentence so far, literal translation would be "[No matter] how [much] [it/they/you] burns, the Kurosumi in [Sourou]!"
^[] around [No Matter] and [much] because while you probably can (and probably should) interpret those words as being there even in literal translation, that's not the only literal translation so not full confidence. [much] as well as [it/they/you] are not included in the sentence, but it is correct that (sometimes) you are supposed to interpret them as being there.
Next you have to translate and insert "Sourou". Possible definitions of the word Sourou:
-The state of things
-Season, weather
-Wait
-Question, investigate, aim for
-"is" or "is there" or "exists"
Now try putting any of those words in the brackets for [Sourou] in the sentence:
"[No matter] how [much] [it/they/you] burns, the Kurosumi in [The state of things]!"
"[No matter] how [much] [it/they/you] burns, the Kurosumi in [Season/Weather]!"
"[No matter] how [much] [it/they/you] burns, the Kurosumi in [Waiting]!"
"[No matter] how [much] [it/they/you] burns, the Kurosumi in [Questioning]!"
"[No matter] how [much] [it/they/you] burns, the Kurosumi in [exists]!"
gdamn you Oda... wtf is this...
I do think it's supposed to be the last definition ("is" or "is there" or "exists"), in which case it's easy to see why the it's easiest to translate this pretty-English-irreconcilable sentence as "The Kurosumi were meant to burn!!!"
but the moral weight that grammar carries is what seems out of place and what we're trying to avoid-- it's not clearly there (BUT IT'S ALSO NOT CLEARLY NOT THERE).
But I do want to give a charitable interpretation... so I feel it's more like...
"No matter how it burns, it's 'Black Coal' after all!!"
Also, I'm going to admit I didn't watch (this part) of the anime where Oden died, and I didn't read the manga in Japanese at all recently, so I didn't even know what the phrase Oden used when he died... so I tried looking it up... and yes it's the same grammar as here. "Niete Nanbono Oden ni Sourou."
And given Oden's carefree nature and bravery in accepting his own death with a smile on, I think it translates very well into "No matter how it boils, it's [just] Oden after all!"
And I added the word [just] here to emphasize the nuance I think is best imparted here. You could translate it as Oden saying that "Oden is meant to boil," but speaking of himself he's clearly not saying he deserves to boil as a moral judgement, but instead that it's obvious that Oden (as in literally the food) is [of course] boiled. Just as a matter of fact, that's how the soup is made and eaten. Just that he's talking about himself, and his death in the same matter-of-fact manner. I add the word "just" here to underscore the point that what Oden is saying is that it's not a big deal for him to boil, he accepts his own death with grace and without anguish or judgement.
Of course the sentences feel different especially after translation because "Oden" is just himself, an individual, and not "Kouzuki" which is a clan of people. There's no genocide against an individual but there can be genocide of a clan. There's not essentialization of an individual based on being himself/herself (you are who your are, living your own life), but there is bigotry/essentialization of characteristics to an individual based on that individual's group membership. A person saying he was "meant to" die this way, sounds really really different (especially in English) from a person saying a whole group of people "are meant to" die this way.
Regardless, if I try to translate Oden's phrase into a clear, colloquial English sentence and also replace the word "Oden" (Japanese hot pot in soy broth) with "Stew" to give us Americans the correct material context, it would be:
"So what if it boils, it IS stew after all!"
Then if I use the exact same grammar for Hiyori's line, it's:
"So what if it burns, it IS black coal after all!"
Which, does sound a lot less genocidal but still kind of gives me the creeps honestly. It is a lot better correctly contextualized and as long as you clearly remember what Oden said when he died, but it's still kind of cringe to me and honestly wished Oda could have come up with a better, morally centered phrase for Hiyori to yell to wrap up the saga.
edit: Also, when I asked my wife (who's Japanese) for her opinion, she said "My English is not good enough, and I didn't study Kanbu (classical Chinese) seriously enough in school to properly answer your question, so I'm glad you interepreted it for yourself. You're probably right."