If I have an item that says: "Engage: Discard any number of cards from your hand to give this item a +1F Token for each discarded card."
Can I use up this engage to avoid passing my Engage action (for some reason) and discard no cards?
Any number...
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.
If I have an item that says: "Engage: Discard any number of cards from your hand to give this item a +1F Token for each discarded card."
Can I use up this engage to avoid passing my Engage action (for some reason) and discard no cards?
You may. If it required you to discard, it would say "one or more".