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, 6 March 2009
An opponent declares an attack against me. I have a Shinjo Isuke in play.
My opponent assigns personnalities to attack province A. I assign my Shinjo Isuke to defend province B.
1. Can I use Isuke's reaction whenever my opponent resolves a battle action at province A ? (What I want to know is: does "If Isuke is defending" implies that he must be at the current battlefield).
2. My opponent plays Sneak Attack and announces the first action. I react by playing Reinforce the Gates. Can I play Isuke's reaction to his action eventhough I negated the action's effects (is the action still considered "resolved") ?
Note: for question 2, if the answer to question 1 is "no", please consider Isuke is assigned at province A.
Brook Cunningham (rules official), 6 March 2009
An opponent declares an attack against me. I have a Shinjo Isuke in play.
My opponent assigns personnalities to attack province A. I assign my Shinjo Isuke to defend province B.
1. Can I use Isuke's reaction whenever my opponent resolves a battle action at province A?
Yes. Reactions are not governed by the Rule of Location, and Isuke is "defending" even though his battle is not the one resolving.
2. My opponent plays Sneak Attack and announces the first action. I react by playing Reinforce the Gates. Can I play Isuke's reaction to his action eventhough I negated the action's effects (is the action still considered "resolved") ?
Yes.
http://rules.l5r.com/Abilities_and_actions#D._Action_resolves: "An action resolves even if all its effects are negated or otherwise do not occur."