Erza from the fairy tale is one of the strongest side characters. Erza's strategic mind and her battle experience make her more versatile than Natsu. She can defeat him at some point too.
Izumi Curtis ( FMAB )
Izumi Curtis is a formidable alchemist and martial artist. She has single-handedly taken down both Elric and Borther several times. Her brute strength and strategic finesse can defeat anyone.
Levi ( Attack On Titan )
Levi is considered as the strongest soldier of humanity. He could take down the most formidable foes, including beath titan. His experience in battle and strength is greater than anyone in attack on titan.
Chuuya ( Bungou Stray Dogs )
Chuuya Nakahara, the gravity manipulator powerhouse and port mafia executive, consistently outshines Atsushi in terms of raw power and combat Skill. He stands as a more potent force compared to Atsushi.
Killua ( Hunter x Hunter )
Killua Zoldyck, a prodigious assassin from the Zoldyck family, showcases extraordinary abilities that often surpass Gon. We still haven't seen his full potential yet but he can be one of the strongest characters in HxH.
Tomura ( My Hero Academia )
Tomura Shingaraki the primary antagonist of MHA evolves into a powershouse with his Decay quirk. He's capable of decaying anyone he touches. With this kind of power, he is a terrifying threat to the whole society.
Beerus ( Dragon Ball )
Beerus the god of destruction is another prodigy in the Dragon Ball series. With his divine abilities, Beerus can effortlessly destroy the entire planet like nothing. Wielding godly Ki that surpasses mortal comprehension.
Gojo ( Jujutsu Kaisen )
Satoru Gojo, the strongest jujutsu sorcerer in jujutsu kaizen, possess godlike abilities that surpass anyone in the jujutsu kaisen universe. His limitless and the six eyes grant him unparalleled control over space and immense curse energy.