Your character’s One Unique Thing (their unique) is a special feature invented by you, the player, which sets your character apart from every other hero. It is a unique and special trait to your player, and markedly unusual. The intent is that it provides a special flavor to the campaign and can assist the GM in determining how your character can interact with characters and story in the campaign.
Your character’s unique should not provide general practical value in combat. That is not the intent. The intent is to open up story arcs and fun roleplaying opportunities