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.
Am I right in saying that this can only be used if I have presence at the current battlefield?
Ninja Battle: Move your target Ninja Personality with no non-Ninja Followers to the current battlefield. You may target a Personality and give him a -1F Poison token.
No you are wrong. Walk in Shadows may be used even if its player controls no unit at the current battlefield because it will move his Ninja Personality to the current battlefield, which matches the exceptions to the rules of Presence and Location (see below).
Exception to the rule of Presence: A player who controls no units at the current battlefield may take a Battle Action whose costs or effects say they are able to move one or more of his units there. The player must then make choices within the action, if possible, such that it does move one or more of his units there, fulfilling Presence.
Exception to the rule of Location: As with the Rule of Presence, a Battle action can target, be performed by, or be taken by a card in a unit at another location if its costs or effects say they are able to move that unit to the current battlefield. The player who is taking the action must take choices within the action, if possible, such that they do move that unit there.