Can I use Oni Mura's battle/open ability if I'm at a battlefield that isn't the one with the region?
Oni Mura
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.
Can I use Oni Mura's battle/open ability if I'm at a battlefield that isn't the one with the region?
This is a vague question. It isn't really clear if the unit involved or the region is the current battle, or if there are other units at the current battlefield, all of which will affect the legality.
If the region but not the unit is in the current battle, it would run afoul of the first part of Rule of Location, because Oni Mura targets a card in a unit, and "Any cards in units must be at the current battlefield to be legally targeted by a Battle action" (http://rules.l5r.com/Battles#Rule_of_Location).
If the unit but not the region is in the current battlefield, that would appear to be legal. You meet Presence by having a unit there, and you're targeting a card in a unit for Location, and the second part of Location isn't relevant.
On: Oni Mura