Demon Slayer is a hit shonen action series taking place in Taisho-era Japan, where flesh-eating demons stalk the night and terrorize humanity. It's up to highly-trained demon slayers like Tanjiro Kamado to fight back, and while the life of a demon slayer is never easy, heroes such as Kyojuro Rengoku the flame Hashira will never complain.
Kyojuro was the star of the Mugen Train story arc, and he proved his worth against the likes of Enmu and Akaza, both of whom are Demon Moons/Kizuki. Given the chance, Kyojuro would gladly fight any other demon from the Demon Slayer series, and indeed, he would take on villains from other anime series as well to defend humanity.
10 Rui Wouldn't Last Long Against Kyojuro (Demon Slayer)
In his own universe, Kyojuro Rengoku is nearly unstoppable, being an elite Hashira who has ferocious flame-based breathing techniques and amazing speed at his disposal. He and the other Hashira will at least stand a chance against the Upper Moon demons, and the Lower Moon demons are in big trouble if they run afoul of Kyojuro.
In the original story, Giyu and Shinobu were the ones who rescued Tanjiro's squad from Rui the spider demon, and they dispatched Rui with ease. If it had been Kyojuro, that fight would have been won even more quickly, and Rui would have never even seen the flame Hashira coming.
9 Yoshikage Kira Couldn't Keep Up With A Hashira (JoJo's Bizarre Adventure)
Yoshikage Kira is a villainous Stand user whose humanoid Stand, Killer Queen, has harnessed the power of explosions. This Stand can touch any object and turn it into an explosive, then set it off at will. Yoshikage can also use Sheer Heart Attack to take the fight to his enemies from far if he must.
All this makes Yoshikage a tough customer for other Stand users, but Kyojuro is a different matter. He can simply ignore Killer Queen and rush right at Yoshikage himself and slash him apart before Killer Queen can intervene. Unless Kira lays the perfect trap ahead of time with Bites the Dust, he's going down.
8 Deep-Sea King's Neck Is Vulnerable (One-Punch Man)
The towering Deep-Sea King may look silly, but he is an incredibly dangerous monster who can even take on the likes of Genos the cyborg or Puri-Puri Prisoner and win if the heroes don't go all out. The King is very tough and has incredible physical strength, and he gets even stronger when it's raining.
If the King doesn't have the benefit of rain, Kyojuro Rengoku stands a good chance of victory. He will take this villainous King seriously and get in close, then use his best flame breathing techniques to take the King's head off. If he pushes himself to the max, he just might be able to decapitate the King in one fell swoop.
7 Combustion Man Is Far Too Slow (Avatar: The Last Airbender)
The silent assassin known as Combustion Man can bend fire with his mind alone and set off powerful explosions remotely to take his enemies by surprise. He has ambushed Team Avatar more than once this way, and he never seems to get tired, either. He's got a brawny physique as well, for when the fight becomes up close and personal.
Kyojuro Rengoku could handle him easily. Combustion Man is too slow to handle Kyojuro's lightning-quick movements, and no explosion would ever get close to hitting its target. Then, Kyojuro would slash Combustion Man to bits.
6 Pakunoda's Revolver Won't Do Her Much Good (Hunter X Hunter)
A few Hunter x Hunter villains would stand a chance against Kyojuro with their remarkable Nen abilities or sheer strength, such as Meruem the Chimera Ant King. However, some members of the villainous Phantom Troupe gang would fare poorly against Kyojuro in a duel if they can't get any backup, such as Pakunoda.
Pakunoda uses her Nen and a revolver to affect her opponent's mind, but she's not going to land a single hit on the flame Hashira. Kyojuro can move faster than Pakunoda can track, and he'll slice her to bits, Nen or no Nen.
5 Aaroniero Arurruerie Will Lose His Heads Fighting Kyojuro (Bleach)
The ten Espadas are Bleach's version of the Twelve Demon Moons, the most elite Arrancars who fight for Sosuke Aizen. They are ranked according to strength, meaning #9, Aaroniero Arurruerie, isn't nearly as scary as the likes of Grimmjow Jaegerjaques or Coyote Starrk. He has some tricks up his sleeve, but they won't work against Kyojuro Rengoku.
In a way, Kyojuro is like a Soul Reaper, a monster slayer with a sword, and he won't have much trouble taking Aaronerio down. Kyojuro could keep pace with Aaroniero's sonido, then break apart Aaroniero's flask and expose his two heads to the open air, killing him. In this fight, Aaroniero won't even get a chance to release his zanpakuto, Glotoneria.
4 Twice Won't Get A Chance To Outnumber Kyojuro (My Hero Academia)
Twice joined the League of Villains so he could find people who'd accept him for who he is, and in exchange for being accepted, he lent his formidable prowess to the League and fought tirelessly for Tomura Shigaraki. Twice can duplicate people, including himself, and he eventually learned to make not only dozens but hundreds of copies of himself.
Twice can mob his opponents as a one-man army, but Kyojuro Rengoku won't let him. Kyojuro's speed vastly outstrips Twice's own, and Kyojuro can slash his way through a whole platoon of Twices and take them all down before they can duplicate themselves again.
3 Kyoya Tachibana's Magical Eyes Can't Save Him (That Time I Got Reincarnated As A Slime)
Some Reincarnated as a Slime villains would be too powerful for even Kyojuro Rengoku, such as Hinata Sakaguchi the vengeful knight, but he could handle any of the Otherworlders who fought on behalf of the Falmuth Kingdom. These three isekai villains are much stronger than they look, but Kyojuro has nothing to fear.
Kyoya has magical eyes that allow him to see his opponent's movements, and he has experience with fencing and swordplay, too. He was even a challenge for Hakuro, but ultimately, Kyoya's skills and talent are not up to snuff. Kyojuro would soon dispatch him with some flame breathing techniques and save the day.
2 Gluttony Can't Keep Up With The Hashira (Fullmetal Alchemist: Brotherhood)
As a homunculus, the ravenous Gluttony has key advantages over regular humans, such as his regenerative abilities and his ability to create a giant mouth on his chest and instantly eat anything in front of him. However, he is rather slow and dim-witted, and he only performs well when backing up a stronger ally, such as Pride or Wrath.
When fighting alone, Gluttony is highly vulnerable to quicker foes like Kyojuro, who could keep slashing him apart with impunity and avoid any return fire. Eventually, Kyojuro would wear out Gluttony's Philosopher's Stone, but Gluttony might retreat before it comes to that. Either way, Kyojuro wins.
1 Kyojuro Can Handle Juzo Suzuya's Speed (Tokyo Ghoul)
The line between hero and villain is blurred and subjective in the story of Tokyo Ghoul, but from Ken Kaneki's point of view, CCG investigators are antagonists, meaning characters like Kotaro Amon, Kisho Arima, and Juzo Suzuya are villains. Kyojuro would take any of them on if ordered to.
Juzo is a quick and acrobatic fellow who can use melee weapons and throw knives, making him a flexible and effective ghoul hunter. Kyojuro could easily keep up, though, and block Juzo's projectiles before catching Juzo with a deadly sword slash to win the fight.