@ThangLong
IIRC being a Sei fighter means to fight in a more calculating manner...being calm and waiting for the right moment to strike, and thus using such techniques as seikuuken and koruinuki (tough spelling!)
on the other hand, a Dou fighter relies more on fierceness, higher rythm and attacks, think Apa and Sakaki
the fact that being dou or sei affects allegiance to katsujinken or satsujinken isn't clear, since combinations have been shown
but still, IMO, a hint is given more than once that dou fighters are more prone to go satsujinken
Lugh being a Sei fighter was a given...he couldn't have possibly been the other way around