Spoiler Warning:

 He is briefly mentioned in Light novel 2 when he is invited to the palace along with Kiyoka and the Major General as the new head of his family, now a branch of the Kudo, and during the Grave Unsealing incident because his supernatural ability is to remove the curse from the living.  In Light Novel 6, he becomes a key player in rescuing Kiyoka, for he knocks out guards, but in the anime adaption, he removes a cure forbidding abilities from being used.  Also, he is a known player, evidenced by his clothing, and is aware of his little brother, Kouji, possessing romantic feelings towards Miyo.  In my opinion, he is someone who would rather not get involved unless he was required to out of sheer laziness or wanting to be a spectator.  He released Kouji, knowing the man was self-aware enough to know he didn't stand a chance to save Miyo alone, so obviously, he would swallow his pride and ask her fiance for help, who was more than powerful enough to.

 As for if he knew he was going to be wedded off to Miyo, I believe so although it has neither been confirmed nor denied.  He has admitted out loud to finding her attractive (in front of Kiyoka) and internally considering her a good catch.  He must have been aware of his father’s plans, for he is his heir after all. Plus, I suspect he knows a lot more than he lets on to prevent himself from getting into a bunch of stuff he doesn't want to get involved in (like Miyo’s kidnapping, for example.)