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.
Can I use it to straighten any Personality, including one without the Cavalry keyword or even one of my opponent's?
The text:
Weapon • Unique Will only attach to a Unicorn Clan Personality. Open: Bow this card: Either straighten or remove Cavalry from a target Personality.
Thank you in advance
Can I use it to straighten any Personality, including one without the Cavalry keyword or even one of my opponent's?
Yes.
The only required target of the action is "a [target] Personality"; not necessarily one that is "Cavalry" or even "your"s.