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, 2 September 2008
Reaction: Reactions may now be taken following an action round procedure. Starting with the active player, each player in turn order has the option to take a Reaction to the trigger or pass. When all players pass consecutively, no more Reactions to that occurrence of the trigger may be taken.
If a reaction on a trigger would make the trigger to disappear, can is still react on the trigger ?
As example:
I have a Shugenja that dies because she is paying a cost. And if have 2 Arihiros [Shiba Arihiro Reaction: Before you destroy one of your Shugenja as a cost: You pay the cost by destroying Arihiro instead. ]
I use the first Arihiro to prevent the Shugenja from dying. Is the trigger still there so that I can react with the second Arihiro ? Or does the trigger disappear at that moment when I use the first Arihiro ?
Brook Cunningham (rules official), 2 September 2008
If a reaction [to] a trigger would make the trigger to disappear, can [I] still react [to] the trigger?
No.
If you use a Reaction to negate an effect before it happens, further Reactions to "before [the effect] happens" are illegal because the effect is not going to happen; the trigger is gone.
http://rules.l5r.com/Timing: "The order of resolution means that effects that come first, due to the above order or the active player’s decision, can negate, alter or render irrelevant effects that come later."