I know that, but other then that single panel (in which he is simply pictured), and the time he was born, he's been a ghost. No mentions, no "screen time", no interactions with anyone else.
I get it, this is a manga about Nana, and now Mana, but Shou has gotten more "screen time" and interaction then even the original side characters (the original couples school mates during school). Hell, at this point I think even Nokki has had more presence then the son.