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, 27 January 2009
Nezumi Vengeance states:
Reaction: If it is the Action Phase, after another player resolves an action that targeted one of your Ratlings with 6 or more Gold Cost, and destroyed him or caused you an Honor loss: Destroy one target Personality who performed the action.
If my opponent Ambushes one of my Ratlings with 6 or more gold cost, and my Rat dies during Ambush's battle resolution, can I play Nezumi Vengeance? Additionally, if my opponent plays a Battle kill action during the Ambush, can I play Nezumi Vengeance because it is technically still the Action phase? My instincts say yes. Thank you!
Edited for spelling in title -Genji
Zen Faulkes (rules official), 1 February 2009
If my opponent Ambushes one of my Ratlings with 6 or more gold cost, and my Rat dies during Ambush's battle resolution, can I play Nezumi Vengeance?
No. The clause "and destroyed him" refers back to the action, and the action did not destroy the Personality. Battle resolution did.
(I)f my opponent plays a Battle kill action during the Ambush, can I play Nezumi Vengeance because it is technically still the Action phase?
Yes. [Reminder to veteran players: Ambush used to say it creates an Attack Phase, but doesn't any more.]