One of my players wants to play as a cursed sword. Wanted to see what you all thought.

So one of my players wants to play as a barbarian who's soul was trapped in a sword and is now capable of taking over the bodies of those who wield him. So far I've made it so that he will have a set of base stats and if he takes something over (through them willingly attuning to him) he gains the racial bonuses of whoever he takes over (only physical he won't know more things). When he's not attuned he'll have blind sense of 10ft and be able to communicate with whoever holds him. And when he is attuned he has full control of whoever he's attuned to. I'm not sure if anything else needs to be balanced. I've asked him to avoid magic but not disallowed it and am wondering if anyone sees any glaring issues with the idea. Thanks in advance!