Since its debut in 2016, Demon Slayer has quickly grown into one of the most popular media franchises in the entire world. Bolstered by the recent success of its anime adaptation and its record-breaking film, Demon Slayer — The Movie: Mugen Train, the franchise has helped usher in a new generation for the shonen genre and is showing no signs of slowing down anytime soon.

Unlike many older titles in the shonen genre, Demon Slayer's narrative moves at a quick pace, so it's easy to miss some of the series' smaller details. That said, the story repeatedly demonstrates that these seemingly insignificant details can end up playing a major role in the fight against Demonkind, making it all the more fun to notice them during subsequent rewatches.

10 Tanjiro's Scar Changes Shape And Size

Demon Slayer's protagonist, Tanjiro Kamado, is one of the most popular anime characters in the world, so even the most casual fans of the medium are familiar with his appearance. Besides his Hanafuda earrings, the character's trademark scar is the most memorable part of his appearance; however, many fans fail to notice that this scar changes significantly during the series' opening sequence.

Tanjiro originally received his scar when he saved his brother from being scalded, but during the Final Selection Exam, this scar transforms from a regular-looking burn mark to the stylish symbol seen on his face throughout the rest of Demon Slayer. Although the importance of this changing scar isn't clarified until later in the series, it's an early sign that Tanjiro has untapped potential.

9 Tanjiro's Fox Mask Foreshadows The Importance Of His Facial Mark

Before Tanjiro Kamado is allowed to enter the Demon Slayer Corps' Final Selection Exam, he is given one final task by his mentor, Sakonji Urokodaki. In order to demonstrate his prowess as a potential Demon Slayer, Tanjiro must first cut through a massive boulder — the largest boulder Urokodaki has ever assigned to one of his students.

During his training, Tanjiro wears a ceremonial mask given to him by Urokodaki, and like Tanjiro's own face, the mask bears a fiery mark on its top left corner. This minor detail may seem like a simple design choice, but as Tanjiro's scar comes to play a larger role in Demon Slayer's narrative, the sunlike markings on his mask take on much more significance.

8 Sabito And Giyu Tomioka Wear The Same Haori

As hard as Tanjiro Kamado tries, he finds himself unable to cut through the massive boulder assigned to him by Urokodaki. Luckily for Tanjiro, the spirits of Urokodaki's former pupils manifest during Tanjiro's training and provide him with guidance, eventually coaching him to the point that he successfully cleaves through the giant rock. However, upon closer inspection, the design of one of these spirits portends a bond that happens later in Demon Slayer's story.

Sabito, one of the two spirits who assist Tanjiro Kamado in his training, wears a green and orange Haori that bears the exact same design as the Water Hashira, Giyu Tomioka's. While it isn't mentioned at the time, Tomioka must have a connection with Sabito, as their shared outfits and Tomioka's pre-existing relationship with Urokodaki are too much evidence to ignore.

7 The Sprites Represent Tajiro's True Heart

During the Mugen Train arc, Enmu was given a second chance to show his worth as a demon. With this, Enmu trapped Rengoku, Tanjiro, Zenitsu, and Inosuke on a possessed train and put them in a deep sleep. Enmu promised a group of children who were living unfortunate lives that he would put them to sleep and give them pleasant dreams if they found each of his victims' cores and killed them. The sick passenger that entered Tanjiro's subconscious was able to find his core, which was the sun.

The Sprites in Tanjiro's dream were just as warm and kind as he is. Even though they knew why the sick boy was there, they guided him to the core anyway. The Sprites are seemingly random gentle spirits that live in Tanjiro's subconscious, but if fans were to count them, they would realize there is a Sprite for each member of his family: his mother, Takeo, Hanako, Shigeru, Rokuta, and Nezuko.

6 Inosuke's Crow Is Absent Because Of His Wild Behavior

The Demon Slayer Corps' war against Muzan Kibutsuji and Demonkind is an uphill, never-ending battle, so its members must stay as well-informed as possible. To do so, they utilize a unique communication system built around Kasugai Crows — strange birds that are capable of speaking complete sentences to their owners.

Although every Demon Slayer is assigned a Kasugai Crow, one character's avian companion is notably lacking from Demon Slayer. Inosuke Hashibara — Tanjiro Kamado's wild, boarlike ally — is so unruly that his Kasugai Crow, Dongurimaru, chooses to avoid him out of self-preservation. This minor detail is hard to notice, but it speaks to just how different Inosuke is from his fellow Demon Slayers.

5 Rui's Spider Family Bear Facial Marks That Symbolize Their Bond

Almost all of Muzan Kibutsuji's twisted creations are dangerous in one way or another; however, few are as powerful as the Lower-Rank Five of the Twelve Kizuki, Rui. The spiderlike demon is a major antagonist in Season One of Demon Slayer, and at all times, he is accompanied by several other demons that he names the Spider Family.

Although it's impossible to miss the demons that accompany Rui, one aspect of their visual design likely slips past fans during their initial viewing. Each member of the Spider Family has a unique pattern that runs across their face, symbolizing both their spiderlike nature and connection to their creator, Rui. As evil as these characters are, their desire to keep each other's company is undeniably touching — a dichotomy that Tanjiro Kamado processes during his fight with Rui.

4 Akaza Scorns Those Who Call Him A Coward

Demon Slayer — The Movie: Mugen Train is the highest-grossing Japanese film of all time, making it an appropriately large stage for the introduction of the Upper-Rank Three of the Twelve Kizuki, Akaza. This fearsome demon is one of the strongest characters in the entire series, and as evidenced by his spectacular fight with the Flame Hashira, Rengoku, he's more than capable of leveling an entire battlefield in the blink of an eye. That said, Akaza does seem to have one small chink in his armor.

As Akaza leaves his fight with Rengoku, Tanjiro Kamado verbally berates the demon in an attempt to goad it into stepping out of the shadows. Among other things, Tanjiro calls Akaza a coward, which clearly strikes a nerve with the powerful villain. Given how little is known about Akaza's past, this small detail seems to be a major clue toward his motivations, so hopefully, it factors into the series' future narrative.

3 Tanjiro Inherits His Hard Head From His Mother

Tanjiro Kamado's father is brought up several times in Demon Slayer, but it's actually the kindhearted Demon Slayer's mother, Kie, who gives him one of his most iconic traits. Throughout the series, Tanjiro repeatedly uses his abnormally hard skull to headbutt his way out of situations, continuing one of the shonen genre's most common tropes; however, it isn't until a minor scene in Demon Slayer's second season that this trait is connected to his mother.

In the post-credits scene of "Never Give Up," the forty-third episode of Demon Slayer, the series states that Tanjiro inherited his hard head directly from his mother, Mie. In addition to this, the episode mentions that Mie once defeated a wild boar by headbutting it, creating a fun parallel between her and Tanjiro, who knocked out the boarlike Inosuke with a similar strike.

2 Muzan Hints That The Blue Spider Lily Is Part Of His Plans

As far as anime villains go, few are as intimidating as the diabolical villain of Demon Slayer, Muzan Kibutsuji. The character is the Father of Demons and archenemy of the Demon Slayer Corps, but despite fighting their ranks for centuries, Tanjiro Kamado and his allies know very little about their motivations. Thankfully, the series seems to provide a small hint about Muzan's master plan.

During Season Two of Demon Slayer, Muzan Kibutsuji briefly asks his subordinate, Akaza, for an update on the location of a strange item: a Blue Spider Lily. Although the purpose of this rare flower is unknown, the fact that Muzan asks one of his highest-ranking demons for an update about its location makes it clear that it's a major part of his plans.

1 Muzan Has A Specific Trigger

When Tanjiro finds Muzan in the Asakusa District in Tokyo, Tanjiro boldly threatens Muzan asserting his goal of killing him one day. Muzan then immediately parts with his fake family and starts wandering the Tokyo alleyways. He happens upon a drunken group who bump into him – Muzan is seemingly unbothered and excuses himself. Upon further provocation from one of the drunken individuals, Muzan loses his temper and kills him instantly. Upon first watch, a viewer might think that Muzan is finally releasing his frustrations from his confrontation with Tanjiro earlier that evening.

However, upon rewatching, a fan will notice that it is what the drunkard said that triggered his bloodlust. The individual stated that Muzan looked "pale" and as if he were going to "fall over dead." Muzan is immediately agitated after hearing this because over a thousand years ago, during the Heian era, Muzan was receiving medicine for an illness that would have killed him before his 20th birthday. Muzan was extremely frustrated at his worsening symptoms. However, he had no idea the medicine was actually working, and it is what led to his demonism. Still, over a thousand years later, any reminder of his weakened body is enough to send him into a blind rage.