These TCG rulings were issued by Upper Deck Entertainment and have since been deemed unofficial by Konami. They were previously considered official and can still be correct, as long as they follow the official gameplay rules, or unless Konami has issued a ruling that says otherwise. References: 
The first effect of "Kamon" targets the card to be destroyed.
If all other "Six Samurai" monsters you controlled were destroyed by an effect chained to "Kamon's" effect, "Kamon's" effect will not resolve.
If "Kamon" declares an attack, then is flipped face-down, then flipped face-up, you cannot use its effect that same turn because it already attacked.
If "Kamon's" effect is used, then "Skill Drain" is activated later, "Kamon" still cannot declare an attack that turn.
These TCG rulings were issued by Upper Deck Entertainment and have since been deemed unofficial by Konami. They were previously considered official, but may or may not necessarily hold true nowadays.
↑The Ruling means that those Rulings apply to all "Six Samurai" monsters with the effect "If this card would be destroyed, you can destroy a[nother] [face-up] "Six Samurai" monster you control instead.", and "Great Shogun Shien".