Besides the compelling storytelling and incredible visuals, Demon Slayer has an intricate fantasy world rich in details. In particular, Koyoharu Gotouge pays special attention to the Demon Slayer Corps' swords. The Demon Slayer Corps receive specially-made swords called Nichirin Blades. Forged from a unique ore that constantly absorbs the sunlight, this is a demon's ultimate weakness. On top of the backstory of the blades, which both the manga and anime highlight in detail, there are also nine different types of blades sorted by color.
The blades change color once handled by their owner, but the owner requires some level of skill to make this happen. Each color imparts different properties on the blades, with the specificities usually matching the personality and skill of the wielder in some form.
The white sword represents Mist, and the user can use skills that focus on obscurity -- hiding in plain sight to swiftly take down demons. The green sword, which focuses on offensive air-powered attacks, represents Wind. Stone-breathing is represented by the gray sword. The pink sword stands out because it represents love, and is derived from Flame Breathing techniques. Inosuke uses the gray-indigo sword, representing Beast Breathing techniques, and it suits him perfectly considering he is quite comparable to a beast in both physical form and attitude.
The yellow sword represents Thunder and is infamously wielded by Zenitsu. Just like actual thunder, when Zenitsu strikes, it's quite surprising and jarring to all. The blue sword represents Water and is the first Nichirin Blade shown in the series, wielded by Giyu Tomioka. One of the most eccentric swords is the red one, which symbolizes flame. Even though much detail is given about all these swords, the black sword, which is wielded by Tanjiro, is shrouded in mystery. It is known that it symbolizes the sun, but there's no information as to what type of skills the user can use.
But is one sword better than the rest? Even though it seems like there should be a stand-out winner, it really depends on the user. Even the worst sword in the right hands could cause damage. The opposite is also true -- a mediocre user with a powerful sword can do wonders. For example, Zenitsu is shown to be mostly cowardly and hesitant in his actions, but when he's asleep, the Thunder Breathing technique takes over, allowing him to rains damage down on the demons around him. Whether that's due to his natural undiscovered talent or is brought forth through the power of the sword alone is up for debate.
The most likely sword to stand apart from the crowd is Tanjiro's black one. Because its full abilities are as yet undiscovered, the potential becomes a powerful thing. With Tanjiro wielding it, it's possible that the black blade will surpass the others due to its own potential, paired with Tanjiro's rising level of skill. The other swords are difficult to rank in terms of power because the wielder brings so much of that power out on their own terms.
Ultimately, no one sword is better than the other (yet). While some are more powerful in more capable hands, the Nichirin Blades are effective and purpose-built, even in relatively unskilled hands. To see these blades in action is to see them in the hands of their proper owners -- the motivation behind the power. As Demon Slayer shows time and time again, it's the will and effort put into the action that determines the outcome, not just the sheer power.