Sou has Asperger Syndrome.
Though, it is a mild high-functioning end of the spectrum. The reason why Sou and Kana have yet to be "in a relationship" is because neither of them want to risk their friendship.
- Or maybe they just see each other as friends.
- Or because Sou is subconsciously trying to prevent Kana from meeting the same fate as Annie, his implied Precocious Crush in the past.
