A topic from AEG's L5R CCG Rules forum, copied for Oracle of the Void from a copy of the forum saved in October 2015, so pages it didn't save are missing. Players' names are left out; the rules officials are named. Rulings are as they stood on these dates; later rulings, the rulebooks and the Rules Archive may differ.
A player, 19 December 2011
Can Know No Fear be used against the reaction of Dragon's Breath Castle? I'm confused on whether DBC'c reaction (Action) is targeting the Samurai personality or if the Attacker is the one targeting the Samurai personality.
Know No Fear
Reaction: After another player's action targets your performing Samurai: Negate his bowing and movement from the action's effects.
Dragon's Breath Castle
Reaction: Even if this card is bowed, after engaging at a battlefield at one of your provinces: The Attacker targets and bows one of his Personalities there.
A player, 19 December 2011
Can Know No Fear be used against the reaction of Dragon's Breath Castle?
Yes. The Samurai is targeted by the Attacker, but he is also targeted by the action from Dragon's Breath Castle, which is taken by the Defender so it is "another player's action" and there is a valid trigger for Know No Fear.