Ryoma build? +Atk -spd

Kill Defiant Atk for Fury, and give him a Spd + 3 seal, as well as Moonbow or Luna, Vantage, and Threaten Spd. That'll give him 38 speed(42 after buffs from teammates.)

Fury, Quick Riposte or Swordbreaker, and then C slot is open for just about anything. You should probably have him carry Reposition or Swap, and then Luna for very consistent damage, or Draconic Aura for equally consistent damage and better kills against squishy units.

I actually have the same IVs on my own Ryoma, so I added a picture of the build I chose for him.

I never completely finished building him (hence the Threaten Atk 1), but he still does very well. This is mostly an enemy phase set that does a good job at finishing off weakened enemies. If you do use this build, you might find it more helpful to run a healer on the same team if you don’t have a combat medic.

My Ryoma is -Atk/+Spd and I gave him Fury, vantage and summoner support so he can reach 52 Atk and 40 spd, you could do the same with yours as he would reach 58 Atk and 37 spd (enough to not get doubled).

You could then increase his speed with the seal speed +3 or count on his OHKO potential and give him the seal attack +3. I use Summer Elise alongside Ryoma with S support so she can give him +10 Atk (support + weapon + rally atk/res + Spur) and +3 speed, when next to him.

You could do the same and increase his OHKO potential (even on counter thanks to vantage) as your Ryoma would go up to an insane 71 Atk when next to Elise (if you don't have Summer Elise it's no problem as any unit can give him +10 Atk as well with the same build, S support and rally atk).