He's not the only new castmember. Tom Hardy ("RocknRolla") has also signed on, joining Leonardo DiCaprio, Joseph Gordon-Levitt, Cillian Murphy, Ellen Page and Marion Cotillard. Not surprisingly, the plot still remains under wraps, but THR reveals that Watanabe will be playing the film's villain, a man who is attempting to blackmail DiCaprio. Hardy will be playing a member of DiCaprio's "team," which should put him together with grad student Page and Gordon-Levitt. Murphy's role is still unspecified.

For more on the growing, comics-friendly cast of Christopher Nolan's "Inception," head over to MoviesBlog.MTV.com.