Seeing Pesmerga and Yuber's clothes I began to think that there was a clan of dark knights. But then after viewing the quote below I realized something...
What if the eighfold rune is shattered in 8 pieces? Each of these Dark Knights holds one of these shards.Maybe they even have to kill eachother and get the shards for themselves (like that movie Immortal or Highlander, can't remember if it was the one or the other.). Yuber and Pesmerga might as wel be the only Dark Knights who have these pieces. Or even killed all the other dark knights for that matter.Kou - means filial devotion
Chuu - means loyalty
Tei - means brotherly affection
Chi - means wisdom
Gi - means duty
Shin - means faith
Jin - means sympathy
Rei - means proper form
Anyway this would change a bit of what you'd think of the 8 parts. Maybe for every new shard one gets conflict with it and has to fight it out. Would explain why Yuber stays evil though his rune seems to embodie pease and stuf.
This might even(strangely enough) make Pesmerga the bad guy (wanting the Rune for his own) with Yuber running away to protect the rune all the time.
Though this is far fetched the main idea behind my theorie makes some sense.