Mysterious Heroine XX is an enigmatic Servant who appears in Fate/Grand Order as an Assassin-class heroic spirit. She is characterized by her eccentric personality and obsession with justice, often speaking in dramatic and comedic ways. Her true identity remains mysterious, though she claims to be a heroic figure from an alternate timeline or dimension. She wields advanced technology alongside traditional weapons and is known for her unpredictable behavior and tendency to pursue what she considers 'justice' in unconventional ways. Despite her chaotic nature, she demonstrates genuine care for those she considers allies and shows surprising depth beneath her comedic exterior.