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, 17 March 2008
1 - If I control Yoritomo Saburo at battlefield 1 and Kitsune Ryukan experienced with a follower at battlefield 2, can I use Ryukan's ability to target the follower at his battlefield and raise Yoritomo Saburo force?
2 - Or maybe target a follower at another battlefield to raise Ryukan's force.
Kitsune Ryukan
Mantis Clan • Daimyo • Samurai • Scout • Experienced • Unique • Loyal Your Personalities with "Kitsune" in their title have +1F. Battle: Target a Follower and a Mantis Clan Personality. Raise the Personality's Force by the Follower's.
Brook Cunningham (rules official), 17 March 2008
1 - If I control Yoritomo Saburo at battlefield 1 and Kitsune Ryukan experienced with a follower at battlefield 2, can I use Ryukan's ability to target the follower at his battlefield and raise Yoritomo Saburo force?
2 - Or maybe target a follower at another battlefield to raise Ryukan's force.
No and no. It's all down to the Rule of Location here, part 1, with a little emphasis of mine:
http://rules.l5r.com/Battles#Rule_of_Location: "The Rule of Location:...
1. Any cards in units must be at the current battlefield to be legally targeted by a Battle action."