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, 11 March 2013
"Essentially, yes. It's the difference between "after another player targets your XXX" and "after another player's action targets your XXX". The former looks for the source of the target, and in the case of DBC it's the Attacker. The latter looks for the source of the action, and it's the Defender. It's particularly relevant when another effects changes targeting, because the change of targeting doesn't change the source of targeting. (You may have made the final choice of what card is targeted thanks to Ryoshun's Guidance, but it's still me who made the targeting.)"
If my opponent targets my personality with a Political action and I activate Ryoshun's Guidance (or Chugo Seido, etc.) as a Reaction, can I no longer activate Daigotsu Toru's Reaction afterwards? (I know he's not ApE legal; he's just the first guy I found with that wording in the Oracle.)
A player, 11 March 2013
You may still react with Daigotsu Toru. Ryoshun's Guidance changed the final choice of target, but not who made the target. If the action told the other player to make it, it's the other player's target even if you made the choice.
From the glossary entry on targeting: A "change to targeting" is anything that changes the target. Choosing a target is different from, and comes before, the actual targeting. Specifically, if an effect interferes with an action so that another player chooses one of the action’s final targets, the player who originally would have chosen the targeting is still the one who targets the final target.