The original manuscript is not completely clear here, but it does seem to read “our lives”. In the ultraviolet photographs of 𝓞, there is some noise between the r and the l, so one could suppose that se had been originally written between these two letters. Nonetheless, the i between the l and the v seems very clear; in fact, the i looks like it was inserted. One possibility is that Oliver Cowdery originally wrote ourselves, erased the se and inserted the i, but this seems an unusual way for him to have corrected a word (by erasing letters in the middle of the word).
This reading (“defend our lives”) would be a unique one in the Book of Mormon text. Otherwise, we get only “defend one’s self ” (ten with themselves, two with ourselves, and one with himself ). Given the prevalence of “defend themselves” and “defend ourselves”, it is not surprising that Oliver Cowdery, when he copied the text here from 𝓞 into 𝓟, wrote “defend ourselves”.
Despite its uniqueness, the reading of the original manuscript here in Alma 54:13 seems appropriate, especially given the semantic contrast between Ammoron’s attempt to “murder us” and the Nephites’ attempt to “defend our lives”.
Summary: Restore in Alma 54:13 “defend our lives”, the apparent reading of the original manuscript.