Nazo Koumori, whose name literally means 'Mystery Bat', is a recurring comic relief character in the anime and manga series Rosario to Vampire. He appears as a small, talking bat who frequently breaks the fourth wall, providing humorous commentary and explanations to both the audience and the characters. Nazo Koumori does not participate directly in the main plot but serves as a mascot-like figure, lightening the mood and helping viewers understand the supernatural aspects of the story.