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, 18 July 2007
Player X announces an attack. I assign my infantray, which included Ikoma Yasuko, to Province A. Player X announces his cavalry to Province B. Player X decides to resolve the battle at Province B, first.
Can I use Ikoma Yasuko's battle action to move one of Player X's units from Province B to Province A during the battle at Province B? Can I use Ikoma Yasuko's battle action to move one of my units from Province A to Province B during the battle at Province B?
Ikoma Yasuko Battle: Even if Yasuko is home: Target a Personality not at the current battlefield. Move him there. If you do not control him, straighten him.
Thanks in advance. For the Lion!
Martin Lund (rules official), 19 July 2007
Can I use Ikoma Yasuko's battle action to move one of Player X's units from Province B to Province A during the battle at Province B?
I wouldn't think so, based on the text you just provided. I'll highlight the relevant portion in Blue Text.
Ikoma Yasuko Battle: Even if Yasuko is home: Target a Personality not at the current battlefield. Move him there. If you do not control him, straighten him.
By definition, a unit in Province B during the battle at Province B can't qualify as "a Personality not at the current battlefield."
Can I use Ikoma Yasuko's battle action to move one of my units from Province A to Province B during the battle at Province B?
Only if Ikoma Yasuko is the unit you target and move. While moving a unit into the Current Battlefield (Province B's battlefield) will get you around the Rule of Presence, the Rule of Location is a greater obstacle.
If a Battle action is on a card in a unit (a Personality or attachment in play), the unit must be at the current battlefield; and any cards in units must be at the current battlefield to be legally targeted by a Battle action.
She's not at the current battlefield, so we need to check the exceptions to see if this is permitted.
EXCEPTION: A Battle Action can target or be taken by a card in a unit at another location if its costs or effects say they move the unit to the current battlefield. Choices within the action must then be taken, if possible, such that they do move the unit there.
So she can use her ability if and only if they move her card to the current battlefield - and you have to make your targeting decision to target her to make the play legal.
Now, Yasuko's ability does say, "Even if Yasuko is home," but you said you assigned her to Province A. If you'd left her at home you'd indeed be able to use her to move any one of your units in Province A to the Current Battlefield at Province B.