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, 1 December 2008
Seppuku reaction says: Reaction: Any number of times per turn, before you lose Honor from an action that targeted or was performed by one of your Courtier or Samurai Personalities: He commits seppuku. If the seppuku destroyed him, reduce the Honor loss to one.
Assuming the action in question was performed by two samurai or courtiers, or was performed by one and targeted another (eg Coward! being played on defense and choosing not to move), would it be legal to commit seppuku with both personalities (That is, two seppukus)?
Brook Cunningham (rules official), 1 December 2008
Seppuku reaction says: Reaction: Any number of times per turn, before you lose Honor from an action that targeted or was performed by one of your Courtier or Samurai Personalities: He commits seppuku. If the seppuku destroyed him, reduce the Honor loss to one.
Assuming the action in question was performed by two samurai or courtiers, or was performed by one and targeted another (eg Coward! being played on defense and choosing not to move), would it be legal to commit seppuku with both personalities (That is, two seppukus)?
Yes, you may.
After the first seppuku, you're still at the timepoint where you can react to "Before you lose Honor" and the trigger of you losing Honor still exists.
This is assuming your opponent does nothing to invalidate the trigger at his opportunity to react to "Before" you "lose Honor" that occurs between your first Seppuku reaction and your second.
EDIT: [This ruling is incorrect. See here.]