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, 26 June 2014
I am crossing my fingers for a "no they don't combo" answer, because Temple's reaction, being repeatable, becomes a little too strong if usable at each province... but anyway:
Temple of Blood's Reaction is:
Reaction: Before engaging in a battle at this Province's battlefield, name a Strategy. While this Holding remains in play, until this battle ends, the named Strategy may not be played.
Whilst Kaiu Sensei reads:
During battles, your non-Unique Fortifications' traits affect each of your Provinces, and you may use such Fortifications' abilities, as if they were attached to the current battlefield's Province.
And yet from the comprehensive (EE) rules:
"Engaging is the time point at which the battle, and the Combat Segment, both begin. Specifically, things that are triggered “before engaging” do not occur in or during the battle, and things that are triggered “after engaging” do occur in and during the battle. "
This paragraph has neither been reprinted (I think) nor revoked in the IvE rules, so I'm not sure if it still applies, but it DOES seem logical...
So is the Reaction from Temple of Blood considered "during battle", and thus usable at every province for a Kaiu Sensei player?
Jon Palmer (rules official), 11 July 2014
I am crossing my fingers for a "no they don't combo" answer, because Temple's reaction, being repeatable, becomes a little too strong if usable at each province... but anyway:
Temple of Blood's Reaction is:
Reaction: Before engaging in a battle at this Province's battlefield, name a Strategy. While this Holding remains in play, until this battle ends, the named Strategy may not be played.
Whilst Kaiu Sensei reads:
During battles, your non-Unique Fortifications' traits affect each of your Provinces, and you may use such Fortifications' abilities, as if they were attached to the current battlefield's Province.
And yet from the comprehensive (EE) rules:
"Engaging is the time point at which the battle, and the Combat Segment, both begin. Specifically, things that are triggered “before engaging” do not occur in or during the battle, and things that are triggered “after engaging” do occur in and during the battle. "
This paragraph has neither been reprinted (I think) nor revoked in the IvE rules, so I'm not sure if it still applies, but it DOES seem logical...
So is the Reaction from Temple of Blood considered "during battle", and thus usable at every province for a Kaiu Sensei player?
No, and the reason is exactly what you cited. The battle has not yet begun when reactions taken before engaging happen.