The following contains spoilers of Demon Slayer Swordsmith Village Arc Episode 1, "Someone's Dream," now streaming on Crunchyroll and Netflix.
Demon Slayer has captivated audiences with its stunning visuals, gripping storytelling, and unforgettable characters. In the world of Demon Slayer, the titular group has been fighting a high-stakes battle for centuries. Their nemeses, the demons, are leagues above them almost in every way, most especially battle prowess. Other than the main antagonist of the franchise, the most fearsome and formidable among the demons are called the Upper Moons. Despite fighting Muzan Kibutsuji for centuries, only recently have the Demon Slayers managed to take down an Upper Moon -- and only the weakest one at that.
Since every demon is a spawn of Muzan, most of them are his underlings. His strongest warriors are the Twelve Demon Moons, which are further subdivided into two. The Upper Moons are the demons ranked from 1 to 6, while the Lower Moons are those ranked from 7 to 12. To become an Upper Moon, a demon must undergo a rigorous selection process and prove their worth to Muzan. This usually involves killing numerous humans (and even other demons) to demonstrate their strength and loyalty to the cause. Now, Demon Slayer has finally revealed the face of Upper Moon One -- and he looks eerily familiar.
Demon Slayer Gives Viewers Their First Glimpse of Upper Moon One
Demon Slayer Swordsmith Village Arc opens just like the previous seasons, showcasing the vast infinity castle. Muzan has once again summoned all the Upper Moons, relaying the death of the lowest among their ranks. Finally, fans of the series get to see all Upper Moons in one place, including the ever-so-agitated Upper Moon Three, Akaza. During their meeting, Akaza is shown becoming increasingly agitated by the presence of the ever-playful Doma, the second-ranked Upper Moon. In a fit of rage, Akaza rips off part of Doma's face. This allows the franchise to introduce Kokushibo, a.k.a. Upper Moon One. He reminds Akaza of the hierarchy within their organization, going as far as cutting the demon's hands.
Kokushibo's character design is very interesting, to say the least. Like the other Upper Moons, he bears semblance to his former human self but with eerie demonic features, notably the fact that his face has six eyes. He has long hair the same color as Tanjiro and flame marks on his face, and wears a purple patterned kimono with a sword strapped on his waist. Obviously, his main weapon of choice is a sword, which he efficiently wielded to put Akaza in his place. His weapon of choice is especially ominous.
Upper Moon One Looks Exactly Like the First User of Sun Breathing
The episode also sheds more light on one of the Demon Slayer Corps' strongest fighters: the first user of Sun Breathing. In a flashback, he is shown conversing with Tanjiro's father, discussing the prospects and future of the swordsman's art, as he doesn't have an heir. This is the exact reason he passed down his unique style to a mere charcoal merchant. That art is, of course, none other than Sun Breathing, the strongest among the styles the Demon Slayer Corps utilize and the original inspiration for all other breathing styles.
Observant viewers will have noticed that Upper Moon One looks exactly like the first Sun Breathing user. Not only does Kokushibo bear the same facial features as the man from the flashback, but he also has similar marks on his face. If it turns out that Upper Moon One is the first user of Sun Breathing, it would be a massive blow to the Demon Slayer Corps. The style is already incredibly rare, with only a select few ever having learned it. The user is said to be the strongest Demon Slayer in history, and no one has succeeded in his title yet. If he did become a demon, then that means he has already acquired Blood Demon Arts. Adding that to the already powerful Sun Breathing means the Demon Slayer Corps are undeniably facing their biggest threat yet.
That said, this theory is not without its cracks. There are numerous instances in Demon Slayer wherein Muzan is shown cowering in the face of this particular Demon Slayer. In fact, Muzan has been so emotionally scarred that he gets scared seeing Tanjiro's hanafuda earrings. All Upper Demons carry this same fear after consuming Muzan's blood. If Upper Moon One is indeed the same swordsman, it doesn't make much sense for Muzan to still fear him. In addition to that, the flashback details the first user of Sun Breathing to have a gripe: not being able to protect what's important to him. This raises another possibility.
Another probability is that Upper Moon One is related to the user of Sun Breathing, likely a close relative. This explains why Muzan's fear is still ingrained in his blood. It also gives the swordsman's sentiments of not being able to save what's precious to him more weight. After all, the strongest Demon Slayer's relative becoming a demon is nothing short of tragic.
If Upper Moon One is indeed related to him, it raises questions about how he ended up as a demon in the first place. Was he forcibly turned into a demon by Muzan or did he willingly choose to become one? In addition to that, there is the question of his motivations. Regardless of the exact circumstances of Upper Moon One's origins, his potential connection to the first user of Sun Breathing poses serious implications for the Demon Slayer Corps. Similar to the earlier point, the fact that he likely possesses Sun Breathing -- based on the markings on his face -- and Demon Blood Art, the power he possesses is beyond the likes of anything Demon Slayer fans have ever seen.