In the entire manga, as far as I have found, Karasuma has smiled exactly once. I didn't even notice it the first time I saw it, but it really leapt out on a second read of the chapter in question. What could this sole indication of emotion reveal about Karasuma's character? Why would he smile right there and then? Was it just a random red herring, or is it the key to everything? Does it have any relevance to his loving Tenma or loving... someone else?
In case you have no idea what I am talking about, the smile (or laugh) was in Chapter 142, page 7. It could suggest one rather shocking possibility that would be the ultimate irony possible in the manga.