So, in the animated series, the elf leader, the first magic emperor, 2 magic emperor wannabes, and one elf leader wannabe are having a hard time fighting and trying to defeat Kotodama devil. Are there official stats for this character? Is Kotodama devil supposed to be the most powerful character in Black Clover?
Although very strong, the Kotodama Devil isn't the strongest entity within the Black Clover verse.
No human characters have been described as being able to beat the Kotodama Devil in a one-on-one confrontation. However, another devil has been described within the universe as stronger than the Kotodama Devil.
A devil named Megicula has been described as globally stronger than the Kotodama Devil by Lolopechka, the princess of the Heart Kingdom. Lolopechka is an extremely sensitive mage able to observe multiple remote locations at once (even in other countries) through ambiant moisture and her Water Magic (augmented by the Water Spirit, Undine). This makes her a credible source (Chapter 228, p.9)