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.
The Sun Returns Interrupt: Bow your target unbowed Tactician. Negate the effects of a Battle or Engage action.
I tried a cursory search about paying costs in Ivory but couldn't find the answer I was looking for. Reading this card it doesn't seem that bowing the Tactician is a cost it's just another effect of the card. If it were a cost wouldn't it read Interrupt: Bow your target unbowed Tactician TO Negate the effects of a Battle or Engage action.
The Sun Returns Interrupt: Bow your target unbowed Tactician. Negate the effects of a Battle or Engage action.
I tried a cursory search about paying costs in Ivory but couldn't find the answer I was looking for. Reading this card it doesn't seem that bowing the Tactician is a cost it's just another effect of the card. If it were a cost wouldn't it read Interrupt: Bow your target unbowed Tactician TO Negate the effects of a Battle or Engage action.
The Sun Returns has no costs. Bowing your Tactician is part of the actions effects.
However, you are required to control at least one unbowed Tactician, as you need one to target otherwise the action cannot be announced.