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, 7 April 2008
During a battle I control personality A at the battlefield 1. My opponent controls personality Z at battlefield 1 and personality Y at battlefield 2.
Can i announce a battle action at battlefield 1 and play Devious explorer targeting personality Y at battlefield 2? If yes, would Devious Explorer negate an action moving personality Y to a battlefield?
Devious Explorer Reaction: After you announce a Battle action: Target an enemy Personality. Your action's effects that move him home cannot be negated. He cannot gain Force bonuses or move to battlefields this turn.
Brook Cunningham (rules official), 7 April 2008
Can i announce a battle action at battlefield 1 and play Devious explorer targeting personality Y at battlefield 2?
Yes. Announcing a battle action satisfies the trigger; as long as there is an enemy Personality at any battle, you can satisfy the required targeting (this part: "Target an enemy Personality."), and that's because:
http://rules.l5r.com/Battles#Combat_Segment: "Reactions are not subject to rules of Presence and Location."
If yes, would Devious Explorer negate an action moving personality Y to a battlefield?
It would negate the Personality's movement. Any other effects of such an action (except Force bonuses, of course, due to the other part of Devious Explorer's text) would still occur.