In Black Clover, there are no stronger individuals than the magic knights, and while each kingdom has its own, the ones fans are most familiar with are those from the Clover Kingdom. Among these knights are the captains of each brigade. The captains have each been promoted to their position for various reasons, one of which is no doubt their strength.
While there's no question that they are each strong, how strong they are compared to one another is still something of a mystery. With multiple rivalries between the captains, it's easy to come up with interesting match-ups, but unfortunately, determining the winner is still pretty tough. Thankfully, after the "Spade Kingdom Raid" arc, fans have a much better idea of what each captain can do and can much more easily determine how strong they are.
Kaiser Granvorka
Kaiser is the captain of the Purple Orcas, replacing the last one after it was discovered he was a traitor. Unfortunately, while much more impressive than his predecessor, he is still probably the weakest of the current Magic Knight Captains. While he does have an impressive amount of magic, further bolstered after he was taken over by an elf, he doesn't have many feats of strength to accurately draw from.
Kaiser uses Vortex Magic, which is much stronger than it sounds. While its main ability is to create whirlwinds, these vortexes are able to deflect or dissipate magic. This makes Kaiser's magic the ultimate shield against opposing mages. However, if one is able to slip through the vortex by erasing their magic, then Kaiser is wide open to attacks.
Charlotte Roselei
It might be unexpected to see her so low on the list, but sadly, the captain of the Blue Roses cannot be ranked much higher. While low on the list, readers and watchers know that in no way is Charlotte Roselei a weak magic knight or bad captain -- it's simply due to how tough her competition is. With unique magic and immense mana reserves, there's a reason that she was able to become a captain.
With her Briar Magic, Charlotte can create and manipulate briars, vines and roses. While it might not seem like much, Charlotte's magic is actually quite powerful and uniquely suited for fighting one of the supreme devils. At a young age, a curse was put on her that caused her magic to lose control and turned her roses blue, and while the curse was broken, her roses remained blue and her magic was weaker than it used to be. After training in the Heart Kingdom, Charlotte managed to regain her more powerful red roses and even managed to turn her blue roses into an anti-curse weapon that absorbs all curses they come into contact with, making her magic perfect against the likes of Megicula or anyone else who uses curses.
Nozel Silva
As the rival to Fuegoleon Vermillion, Nozel Silva is one of the strongest mages in the Clover Kingdom and has mana reserves roughly equal to him, making him incredibly powerful even without looking at his spells. While his magic is weak against his rival's, Nozel proves how strong he is by still being able to fight against Fuegoleon on equal footing.
As a practitioner of Mercury Magic, Nozel has one of the unique magics of the captains. Thanks to a perfect mixture of his mother's steel magic and father's water magic, Nozel can essentially wield a dense metal with the flexibility of water. This powerful combo can be downright deadly, as mercury is an incredibly poisonous metal if it gets into someone's body or blood. Nozel can even render Light Magic useless by making his mercury smooth and compressed enough to reflect it back at the user.
Rill Boismortier
Another character that might be surprisingly low on the list, Rill Boismortier is the current captain of the Aqua Deer. While both the youngest current captain and youngest of all time, Rill definitely earned his position by being one of the strongest mages in the kingdom with one of the most unique kinds of magic that exists.
With his Painting Magic, Rill can pretty much paint anything he wants into existence. If that wasn't enough, he can even paint elemental attributes, making his magic incredibly versatile and infinitely customizable for any situation. The only weakness that his magic has is that it's tied directly to his emotional state. If he's happy and feeling creative, Rill is practically unstoppable, but if he's feeling down at all, his magic is hindered immensely.
Fuegoleon Vermillion
While some fans might believe he deserves a different spot on the list, the current captain of the Crimson Lions has earned his position. While being comatose for a large part of the series, when he has appeared, he has always left a strong impression. Utilizing Fire Magic like his siblings, his power and potential were so great that he was even chosen to be the master of Salamander, the Fire Spirit.
With his Fire Magic, he has proven strong enough to face elves in single combat without even relying on his Fire Spirit. According to other captains, he is incredibly strong and has even earned the respect of his sister Mereoleona, and he is capable of focusing his fire into a laser beam of flame to decimate foes. After losing his arm, he's managed to use his mastery over Fire Magic to replace it with one made of pure flames. Quite frankly, if he had shown any mastery over Spirit Magic, such as Spirit Dive or the ability to achieve Saint Stage like Noelle, he'd be even higher on the list than he already is, but he has not shown that he can just yet.
Dorothy Unsworth
Dorothy Unsworth is a unique mage in the same way that Rill is. Much like her fellow captain, her Dream Magic doesn't have a set elemental attribute and is completely versatile in that regard, but somehow even more dangerous. Her Dream Magic lets her trap opponents in a dream world that she manifests. In this world, Dorothy can pretty much create and manipulate anything she wants and is completely safe from any attacks from someone not inside the dream world.
While she cannot control the magic of those caught inside, the dream world causes those trapped to feel increasingly drowsy. If her foes were to fall asleep inside the dream before finding an exit, they would never be able to wake up again, making this magic incredibly powerful and almost unbeatable. She's even able to read the minds of others both inside her dream world and out, making it hard to sneak up on her.
William Vangeance
As the captain of the first-ranked squad, William Vangeance has appropriately powerful magic to go along with his position. With his World Tree Magic, William can create and manipulate giant trees. While this might not sound as impressive as something like Dorothy's Dream Magic, William's trees can absorb the mana from anyone or anything ensnared by them, greatly increasing his own reserves.
William's magic is incredibly versatile too. Not only can it be used as a way to strike or trap opponents, but it can also be used for defense and healing. While unable to defeat Zenon of the Dark Triad, his World Tree Magic did prove strong enough to block and restrain some of his attacks while also being able to heal and stabilize all of his squad members who were on the verge of death. It's a "thinking man's" magic, which works incredibly well for William.
Jack the Ripper
The exact opposite of Vangeance's magic, Jack the Ripper's Slash Magic is as straightforward as it gets. Jack is able to generate magical blades anywhere on his body that he can use to cut down opponents. While this might seem very underwhelming and maybe even the weakest magic on this list, manga readers know better than to underestimate Jack.
The true strength of Slash Magic is its adaptability. While fighting, Jack's blades adapt to his opponents and the specific battle, getting stronger the longer the bout lasts. With this ability, Jack has been able to cut through offensive spatial magic that would have normally erased whatever they came into contact with and even intangible concepts like gravity. He can even cut through an opponent's regeneration abilities, making the wound harder to heal from. While simple on paper, this magic allows Jack to potentially beat any opponent as long as he's able to continue fighting, placing him -- however narrowly -- in the top five.
Yami Sukehiro
Yami Sukehiro is easily one of the strongest people shown in the series so far, being beaten out by only a handful of individuals. With his unique Dark Magic and battling style, Yami brings a whole different kind of fighting to any conflict.
His Dark Magic might be slow in nature, but it's devastatingly powerful. Yami can use his magic to completely absorb magical attacks directed at him, acting almost like a pseudo-anti-magic. Offensively, Yami can use his darkness to enhance his swordplay by creating giant slashes of Dark Magic, some of which can even cut through dimensions.