It's probably no surprise that the series in question is Kamigami no Asobi, and it involves Takeru and the way he addresses Tsukito. He calls Tsukito "Anii." Because that's how Crunchyroll rolls (ha, ha, ha), it gets translated, in this case, not inaccurately to "Brother." I always tend to cringe a little when the familial terms get translated like that, because we usually just don't talk that way in English...although in Burn Notice, Sam calls Michael "Brother," and they're not even related, so I guess it could work in the right context. (You see how we're using Burn Notice as a linguistic standard these days? I'm not sure that's a good idea, but it certainly isn't a terrible one. Only problem is we watched the last episode of Burn Notice last night, so we need to find a new TV show to tell us how the cool kids are talking these days.)
But speaking of familial terms, we do tend to call our cousins, for example, Cousin Jonathan, and in one of the Sherlock Holmes novels there was a character who called his brother Brother...whatever his name was. Like Brother John or something, and he wasn't a priest. So clearly it used to be a thing, but that was like a hundred years ago. Still, since we're dealing with mythology, archaic language isn't technically a problem.
The problem is lack of context. We probably would have made the same mistake if we had been assigned the series and not already played through the whole game. See, Anii is not a typical form of address. The first hint is in Apollo's story, when all the gods are setting up a party for Apollo. It was really funny, actually, because Takeru is talking to Tsukito and Yui comes up, at which point Takeru freaks out and is like, "Did you hear that?" "Uh...hear what?" Tsukito explains that Takeru is self-conscious about other people hearing him call Tsukito "Anii." And Yui is like, "Um, I'm pretty sure I've heard him say 'Anii' several times in public..." But there you go.
The reason behind Takeru's self-consciousness is revealed in Tsukito's story. The first time the two of them form a brotherly bond, Takeru, who is easily moved to tears (that's his special character quirk, like Apollo constantly repeating himself), tried to call Tsukito "Aniki," but he was crying so hard it came out wrong. And apparently it just stuck after that.
In other words, an articulate "Brother" becomes an inaccurate translation in light of the context.
If it had been us, and it had been our job to translate Anii instead of just leaving it, we probably would have done the exact same thing. And then we would have found out the context and been like, "D'oh." And that's one more reason we tend to prefer not translating forms of address.
Today I'm thankful for getting to watch all of Burn Notice, getting to watch Yozakura Quartet afterward when we were like "Aww it's over!" and needed something to cheer us up, the full version of the ending theme to the KamiAso game, getting a shipping confirmation from Kinokuniya, and Page being super cute even if she is on the laptop keyboard.