"He borrowed a heart?" Wouldn't that be like... stealing someone's soul? Can you 'borrow' those? Add doesn't sound very convinced.

"If it's borrowing, then that would mean he removed the ability from someone else so he could inherit it for himself. If you also inherited an ability in this way that he currently has simultaneously, that wouldn't be 'borrowing'. Perhaps the term you mean to use is 'sharing'?"

... Although, the idea of sharing a soul doesn't sound any less ridiculous.