The following contains spoilers for various anime, such as Naruto and One Piece.
With every hero comes a sidekick. Even though heroes play an essential role and are the central focus of an anime, sidekicks are just as important. Along with acting as combat support for heroes, sidekicks can also be comic relief characters. In addition, sidekicks have their own goals and internal struggles, whatever they may be, apart from the hero.
Some anime sidekicks are so powerful that they surpass the main characters in strength. However, this is not always the case. Often, sidekicks are there to balance the heroes and be what the hero is not. That said, here are eight of the most powerful sidekicks in anime.
8 Alphonse Elric - Fullmetal Alchemist
Alphonse (who often goes by Al) is the younger brother of Edward Elric, the main protagonist of Fullmetal Alchemist. After the resurrection of their mother through alchemy fails, Al loses his body, and his soul gets transferred into a giant suit of armor. It becomes his mission (along with Edward's) to find a way to regain his body and his brother's limbs.
Although Al is just a young boy, he becomes quite strong due to his metal suit of armor. He is also a skillful alchemist, though not as adept as Edward. However, his strength and size make up for this. Al and Ed make the perfect team because they balance each other out.
7 Nezuko - Demon Slayer
Nezuko is a demon and the younger sister of Tanjiro, a demon slayer. After Nezuko gets turned into a demon, she behaves like any other demon. However, when her brother protects her from a demon slayer, something inside her switches, and she becomes quite protective of him.
As a demon, Nezuko is one of the most powerful sidekicks in anime, despite her quiet demeanor (perhaps due to the muzzle she is always wearing). Along with excellent fighting hand-to-hand combat skills, she is exceptionally strong. Additionally, she has the ability to change her own size, control blood, and regenerate, among other things.
6 Genos - One Punch Man
Genos appears in the second episode of One Punch Man. He is a cyborg (also known as the Demon Cyborg) whose mission is to find the cyborg that killed his family when he was still a regular boy at fifteen. After witnessing Saitama's raw strength, he asks him to be his mentor. After Saitama agrees, Genos pledges his loyalty to him.
Genos is quite strong due to his mechanical parts but has yet to master his skills. For example, he almost always comes out of a battle scathed. Genos is evidently no match for his mentor, but his training as Saitama's disciple gets him closer to his ultimate goal of avenging his family.
5 Migi - Parasyte
Migi is an alien and a parasite that targets Shinichi Izumi one night. However, after being unable to consume Shinichi's brain, Migi invades his right hand. Migi also doesn't feel or understand human emotions. But what it lacks in feelings, it makes up for in strength (and eventual loyalty).
Migi is exceptionally powerful when it has a host. It can shift into different weapons, objects, and other things. It also has the ability to heal Shinichi's wounds and combine his strength with Shinichi. However, without a host, Migi could die. As a result, it can't detach from its host for too long.
4 Kakashi - Naruto
Kakashi Hatake is known to be one of the most powerful characters in Naruto. His immense skill and strength make an appearance early on in his life. After his father died, Kakashi became adamant about following the Shinobi rules precisely as they were. However, this meant that others didn't like working with him because he was strict.
Kakashi has mastered countless Jutsu, including Chidori, Rasengan, and Raikiri (a stronger form of Chidori). At one point, Kakashi loses his Sharingan during the Fourth Great Ninja War, which is a huge loss for him, as he is known as 'Kakashi of the Sharingan.' However, he perseveres and creates Shiden to rely on instead, exhibiting his immense skill and talent.
3 Zoro - One Piece
Roronoa Zoro appears in One Piece very early in the series (the second episode, to be exact). He is the first person to join the Straw Hat Crew after Luffy asks him, making him Luffy's sidekick. Zoro is one of the most powerful sidekicks because of his swordsmanship.
To say that Zoro is an exceptional swordsman is an understatement. He is so incredibly skilled that he created the Three Sword Style, a technique of handling three swords: one in each hand and the third in his mouth. He is also one of the twelve pirates classified as the Worst Generation, and one of the two pirates of the Worst Generation not to be a captain of a crew.
2 Krillin - Dragon Ball
Krillin is perhaps one of the most well-known anime characters, as he was introduced to Dragon Ball viewers in the 1980s. Krillin is an exceptionally skilled martial artist, and one of the most powerful ones in the franchise, which is quite impressive because he is human, unlike other warriors who are Saiyans.
As a trainee under Roshi, Krillin started out as competitive, particularly with Goku. However, they eventually become best friends. In addition, Krillin becomes Goku's sidekick and a comic relief character; therefore, his strength is not always fully represented accurately. On the other hand, if he were made to be the opposite, perhaps he would have been taken more seriously.
1 Killua Zoldyck - Hunter x Hunter
Lastly, Killua is absolutely one of the most powerful sidekicks. His innocent appearance counters his immense skill, power, and strength. After Killua meets Gon Freecss, the protagonist, he tells him he escaped his assassin family. Eventually, they become best friends.
Coming from such an intense family, Killua is obviously not an ordinary boy. Despite his very young age, he was trained to be an assassin like those in his family. However, his time spent with Gon is somewhat of a reminder that he can be normal. While he can be intense, he can also be quite cheerful. He also enjoys sweets, just like many children, which reminds the audience that despite all of his training, he is ultimately still a young boy.