Hey dU,
Even if the general were dead, isn't it common practice to assimilate them into other armies? Like some parts of Ou Ki's went into Tou's and Duke Hyou's to Hi Shin's. His secrets must be known to atleast some people...
Well Ou Sen's aura lies in his mystery. Besides he had to General against Ri Boku. On top of that Ri Boku was very well prepared and had an overwhelming advantage.
Well people's humanity is dwindling both in real world and in MC's world. Common sense too.
Edit: I wonder why did they chose this manga for anime adaptation...
Well he had motivation back then. Revenge for Ou Ki and Duke Hyou.
Besides I believe Lightning Charge was also a specialty of the Ou Ki Army. He used it to take out Enemy Generals Head though. Rakuakan instead is using it indirectly...Nice Nice.