I've only seen one thing talk about their backstory (I don't even remember where from) and it said that they're the fourth/fifth member of Team 7.
Is that true or are you something else? From what I've gathered through playing, it feels like you're an Anbu-in-training (getting missions from Anbu Captain, going around and working with other teams, doing solo missions, etc.), kind of like how Sai's in Root, which would be totally awesome. Plus, that would have more lore-following than being the extra, fourth member on the 3-man team.
But I don't know, that's just my hypothesis based upon what I view as evidence for my idea. I really just want this question answered, haha.
Bee tee dubya, love the game, super-fun, Crimson Fist is so awesome. ♥
(if this is the wrong place to put this thread, please tell me! It just seemed correct)