I ended up using the following runes on Riou:
H - Spark - allows other party members to attack after bearer
Rh - Bright Shield
Lh - Mother Earth
You can get the Spark rune from the Double Head, the boss at the Sindar Ruins. I used to put it on Nanami, but took it and placed on Riou just before re-taking Rockaxe, because you will lose whatever you equip on Nanami forever once she 'dies'. Spark is a good rune for him if you want to auto-battle every time with strong melee attackers like Sheena and Killey, much more for slower but stronger characters. It is because Riou is faster than most people in the game, only defeated by Nanami, Luc, Stallion, and probably Tir.
Mother Earth, hmm... Riou has the Bright Shield Rune anyways, so I might as well make him my main supporter, while making the rest of the party do the dirty work. For Riou has better affinity to support magic runes than the offensive ones. A B in Resurrection would mean that if equip him with it, plus a Mother Earth rune, Riou can become a very effective FS (Full Support) character. Heh, so much for an FS Main Character. There aren't those kinds of heroes around. Most heroes are fighters, so why not try make the Hero the Main FS?
It's not all about knowledge, but it helps.