Neutral is very important in this matchup. Most of the valkenhayns I've played tend to rush in with 6d, but Terumi's 5A beats that completely. Valkenhayn has poor mobility compared to most of the cast, so play neutral until you can get in, and once you do, continue to pressure him. Just like Axle said, he's about as bad under pressure without meter as we are.
However when he has meter, watch out for his 632146D. This is really his only reversal besides Counter Assault. Just pay attention and block it if they use it as its extremely punishable.