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.
As a Focus Effect, the duel's winner may take an additional action.
Charm's focus effect grants you an additional action, but it does not precise what type of action it is. It is usually obvious, but here goes tricky situation.
Let's focus Fortune's Charm in CooaT duel issued during engage segment thanks to Open Emotion. If I win duel, do I get additional Battle (same type as action that created duel) or Engage (appropriate to current phase/segment) action?
Since the Charm doesn't specify which type of action, and doesn't force you to use a specific ability, it must be an action approppriate to the phase / segment.
Before you bring the inevitable follow-up, let me clarify that the ruling on Come One at a Time doesn't extend to Fortune's Charm because the wording of COaaT is very precise on what action can you take as an additional action ("Take an additional action granted by (this card)"), while Fortune's Charm is not. Therefore you can't claim that the Charm is directing you to use a Battle action in the Engage Segment, because it does not. You are free to take any Engage action available to you, but only Engage ones.