Puzzle wrote:- Sin in FF10 is an entity that absorbs people to control them (correct me if I'm wrong - I googled that up).
Not true. According to Yevon's teachings (religion in FF10), Sin is the incarnation of the failings of humans. It is a massive beast, a possessed aeon, killing everything in its path. There are a few other details about Sin which could give clues about some details of its role, but without the existence of two or three other FF10 roles, I doubt that these details would exist. So I'd say that we could simplify Sin to the bringer of destruction.
Oh, I almost forgot about the toxin. When Sin attacks, if there are any survivors, they are exposed to Sin's toxin. This toxin sometimes provokes a type of amnesia. This could also be an ability of Sin's role, if that role exists in this game.