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 May 2008
So I play an Ambush, targeting one of my nonhuman personalities and something squishy-looking my opponent has. He Refugees himself, Seikitsu Mountains, Stay Your Blade, or whatever, and sends himself home. I play Surprise Attack targeting that personality. At the original Ambush battlefield, my opponent and I both pass our actions and the battle ends without any units there.
What happens next? The current wording of Ambush does not create an attack phase and the only reason you resolve a battle there is that Ambush tells you to. So as far as I can tell, there is no card or rulebook effect telling you to actually fight the battle created by the Surprise Attack. Do the personalities in the Surprise Attack battlefield hang around until a player declares an attack and a battle is forced to resolve in that province? If so, and the attacker/defender positions are switched (i.e. my opponent is the next person to declare an attack), who is the attacker and defender, the attacker and defender of the current attack phase or the attacker/defender assigned by the Ambush?
Alex Jones (rules official), 6 May 2008
So I play an Ambush, targeting one of my nonhuman personalities and something squishy-looking my opponent has. He Refugees himself, Seikitsu Mountains, Stay Your Blade, or whatever, and sends himself home. I play Surprise Attack targeting that personality. At the original Ambush battlefield, my opponent and I both pass our actions and the battle ends without any units there.
What happens next? The current wording of Ambush does not create an attack phase and the only reason you resolve a battle there is that Ambush tells you to. So as far as I can tell, there is no card or rulebook effect telling you to actually fight the battle created by the Surprise Attack. Do the personalities in the Surprise Attack battlefield hang around until a player declares an attack and a battle is forced to resolve in that province? If so, and the attacker/defender positions are switched (i.e. my opponent is the next person to declare an attack), who is the attacker and defender, the attacker and defender of the current attack phase or the attacker/defender assigned by the Ambush?
See: After Resolution.
"If one or more battlefields remain that have not resolved or ended a battle, repeat the battle procedure starting with Choose Battlefield."
After the resolution of the battle at the battlefield created by Ambush, you choose the battlefield created by Surprise Attack and fight a battle there.