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, 13 February 2012
Situation:
mantis player attacks Aroru defends,
Mantis uses naval invasion reaction and target Aroru with Stronghold battle to move him home
Can I use Aroru reaction to jump back to the battle?
Suitengu's Torch Thunder Reaction: After you announce a Thunder Battle action: Its effects will n ot be negated or delayed. Battle: Choose your performing unbowed Personality and target an enemy Personality: Move him home.
Shosuro Aroru (Experienced 2) Scorpion Clan • Ninja • Duelist • Experienced 2 • Unique Will not attach non-Ninja Followers. Reaction: When an action would target a Ninja at Aroru's location: Choose another of your cards. The action targets it instead, if legal. After the action's resolution, you may move Aroru to a different location. Battle: Other players may not take Reactions until this action ends. Ranged 5 Attack.
Jon Palmer (rules official), 13 February 2012
Situation:
mantis player attacks Aroru defends,
Mantis uses naval invasion reaction and target Aroru with Stronghold battle to move him home
Can I use Aroru reaction to jump back to the battle?
Suitengu's Torch Thunder Reaction: After you announce a Thunder Battle action: Its effects will n ot be negated or delayed. Battle: Choose your performing unbowed Personality and target an enemy Personality: Move him home.
Shosuro Aroru (Experienced 2) Scorpion Clan • Ninja • Duelist • Experienced 2 • Unique Will not attach non-Ninja Followers. Reaction: When an action would target a Ninja at Aroru's location: Choose another of your cards. The action targets it instead, if legal. After the action's resolution, you may move Aroru to a different location. Battle: Other players may not take Reactions until this action ends. Ranged 5 Attack.
Yes, if you use Aroru's reaction in this case, and choose an illegal target, Aroru will remain targeted, be sent home, and after the action's resolution you may move him back into the battle.