without seeing the original Japanese or having any reliable knowledge of the Japanese language, I'm guessing he meant to say something to the effect of him being able to switch from one skeleton to the next, since we've seen him body hop before? It'd make it relatively pointless to destroy his physical body when he can just use another skeleton in the vicinity.
Raw is "私の体は只の器だ" ("My body is a mere vessel"), so it looks like their MTL misread the "只" (just, mere, nothing but) as "兄" (brother).
The funny part is that it's one of the only words in the whole chapter to have furigana (found four on a quick skim), so it's probably the easiest word in the whole chapter to understand.
Edit: Oof, missed a whole page of comments there, but I guess the furigana part is still interesting even if I am last over the finish line.