You have never thought of Natsume having such a thing as an 'Alter Ego', but here we are. You have noticed some minor changes, but brushed them off. There was a rumor in Yumenosaki Academy that someone threatened the Delinquents so bad they were scared to talk to anyone, and all the clues led to Natsume. You never knew, but Sato, who was his supposed 'Alter Ego', only did that to protect Natsume and others. But of course, they both remember that.