This is a little old school: Does Ninja Thief target? I know it does not say target on the card, but its an older card and things have changed. The question involves using Investigation after someone else uses Ninja Thief.
Ninja Thief
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.
Does Ninja Thief target?
In Legacy, http://rules.l5r.com/Older_Cards#For_ca ... THE_EMPIRE: "An action targets whenever it requires a choice to be made of what card it affects, or what card pays the non-gold costs of the action."
Let's see, was it last printed before Dawn of the Empire? Yes, in Diamond Edition. It targets.
On: Ninja Thief