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 the current battlefield has a region attached then I play black hearts, red blades. Does the region get discarded too?
relevant texts:
Black hearts, Red blades:
Ninja Battle: Target two of your unbowed Ninja Personalities without non-Ninja Followers: Move them home. If both of them moved, discard any cards in the current battlefield's province and draw two cards.
If the current battlefield has a region attached then I play black hearts, red blades. Does the region get discarded too?
No. Black Hearts, Red Blades discard any cards in the current battlefield’s province but the Region is not in the province, it is attached to the province. An effect that discards any cards attached to a province will explicitly says so; for example see Burned Village, a Strategy card from Glory of the Empire.