Life, the universe, and everything

Dusk Shine. Think about it. How else could Midnight have "Twilight"'s genes?

Now that that's out of the way, he is another character that serves little purpose in SatN for various reasons. Firstly, characterising him would consume too much space for almost no gain. Also, Midnight does love him, but cares little about him. Thus, to reflect her perspective in the fic, he has a very low presence and is never described as she never inspects him. Also also, she is very independent and trusts almost nopony, especially when still in Canterlot, which means that she draws little on him to outline that.

... little else. Basically, he's a walking plot element.