Keen Gronwolf+ Soren help

I think Fury/Green Tomebreaker could be a good option. That way he will check cavalry units and duel blue/green mages easily. C skill and sacred seal is flexible. An example would be an Attack/Defense Ploy combo to bring long-range support to his team. Moonbow/Glimmer or Iceberg as special. You can run Glacies too to make up for the attack bane if you're going to use QP seal on him or want him to have an Infantry Pulse ally on the same team, but I wouldn't recommend it in case he's not going to be able to get his cooldown reduced in some way. As for support skill, Draw Back is probably your best bet, but other options like Swap or Reposition can work just as well.

Good luck with your boy!