There are words that can work. I don't know about others, but I always felt "comrade" was a very powerful word. Crewmate and "mate" are pretty good as well.
IMO, the problem with the words 'Comrade' and 'Mate' specifically is that they're weighted with other meanings. Perhaps I'm alone in this, but I tend to think of 'Comrade' as the term that the Stereotypical Evil Red Communist Russian (circa 1956) would use to refer to anyone on his team, and 'Mate' immediately makes me thing of annoying Australian stereotypes. That doesn't mean that there aren't other words that would work.
I suppose the most effective transfer of meaning would be to say something like "Nami, you are my (friend)+(crewmate)+(semi-familial related)!" but that would be hardly poetic.
Honestly, the only reason non-speakers find "nakama" to be so powerful and meaningful is because they have little exposure to the language and believe the word to be more meaningful than anything in English.
I also think, as suggested above, it's a punchy way to refer to something that would otherwise warrant a non-punchy explanation.
And I like how dythim posted in this thread without trying to accept accountability for this cancer he unleashed into the fandom, and subsequently others.
At least it gave fantards a word other than 'kawaii' to say.
Aside: can someone explain to me why the standard picture of a weaboo is a man holding what appears to be a club? Shouldn't it be a zitty kid with a Naruto headband and enough Pocky to build a log-cabin sticking out of his bloated maw?