All the demons of Kimon shared the same weakness: OVERCONFIDENCE

Which made them careless and thus vulnerable:
- They all resort first to their superpower (instead of saving it as last resource) and rely almost exclusively on it, not even bothering to dodge/block attacks or even have a plan B.
- They all give up the element of surprise by precisely using their powers right from the start.
- None bother to even think that their skills do not make them invulnerable nor invincible, and in fact can be used against them.

Even the blind swordsman, let his ego get the better of him (saving both Jubei and Kagero just to duel him knowing Kagero won't just stand still, when his mission was KILLING them, not dueling them).

Or Jurimaru, the most cautious one, slighting the woman with the explosives and killing Benasato over jealousy, he was begging to be back stabbed.

Or Gemma, charging with no sword against Jubei, challenging fate until he got what he was looking for: an inescapable death (lake of molten gold).

Idiots all of them.

Jubei, Kagery and the old man on the other hand, always resorted LAST to their powers, thus gaining the upper hand and surprising their enemies.