In Demon Slayer, the best of the best sometimes manifest a special marking on their body, known as a Demon Slayer Mark. These mysterious marks bestow great power that comes at a price, and not every Demon Slayer can get one. They also vary from person-to-person, and don’t manifest in the same way for everyone. Here’s everything fans need to know about the Demon Slayer Marks, explained.

Put simply, a Demon Slayer Mark is exactly what it sounds like–a mark that identifies one as a Demon Slayer. However, these aren’t some kind of brand or tattoo. Instead, Demon Slayer Marks sometimes appear suddenly on slayers in the heat of battle. They often last for a short time, but always appear in the same pattern, which can differ between different people. The marks are influenced by the slayer in question’s preferred Breathing Style, such as Tokito’s, which vaguely resembles fog rolling in to match his Mist Breathing. The Demon Slayer Mark also has a major downside, however.

Demon Slayer Marks Are a Blessing And a Curse

In order to activate a Demon Slayer Mark, it’s necessary for the Slayer to reach certain physical states during battle. After Tokito activated his Mark, in chapter 129, he relayed his condition to the others: a heart rate of 200 BPM, and a body temperature of 39 degrees Celsius (102.2 degrees Fahrenheit). That’s a potentially deadly fever and a very unsafe heart rate, and Tokito speculates that the key to unlocking the Mark is simply surviving these conditions. The Mark, however, enables slayers to activate the Red Nichirin for their swords, which drastically increases their demon-slaying ability, improves one’s physical strength and endurance, and even provides access to the mysterious “Transparent World.”

After learning about the Marks, the Hashira almost universally agree to try to obtain one for themselves, however it turns out there’s a high price. Stories about the Demon Slayer Mark from the past indicate that those who manifest a Mark will not live past the age of 25, except for the original Mark holder Yoriichi Tsugikuni, who lived to 80. People over 25 can manifest the Mark, but it’s unknown what the consequences of it are. In essence, activating a Demon Slayer Mark means trading away one’s life and future for power in the present, and unfortunately, there’s no reversing this, as even a brief activation of the Mark is enough.

Why Yoriichi Managed to Live Past 25 After Activating His Mark

It’s never fully explained why Yoriichi is the only demon slayer who was able to live a long life despite having a mark. It’s implied that this may be due to the fact that he was born with the mark, rather than unlocking it later in life. Since Yoriichi had a mark since birth, he was capable of some truly incredible things, like his ability to use the “Transparent World” technique from a young age. The mark may have even influenced his ability to develop the various Breathing Styles seen throughout the series.

It’s said that one individual will always manifest a mark first, before it then begins appearing on those around them, and it’s possible that this might also be why he survived past 25. If so, that would be good news for Tanjiro, as he was the first of the Taisho-era demon slayers to manifest a mark. Tanjiro’s mark also happens to be nearly identical to Yoriichi’s, and he did have the scar present in that location before the Demon Slayer Mark appeared. Tanjiro’s father had a birthmark in the same spot, suggesting that the mark is passed down genetically as well.

It’s stated by Rengoku’s father, Shinjuro, that all people capable of using Sun Breathing have the same mark on their forehead in the same spot, suggesting that Tanjiro always had great potential as a Demon Slayer, as presumably his father did before him. This would explain why Tanjiro’s father was capable of the Hinokami Kagura, even if he didn’t understand that what he was doing was derived from Sun Breathing. This also seems like a good sign that Tanjiro might be able to evade the Mark’s curse as Yoriichi did.

With that knowledge, it’s certainly a bittersweet moment for fans to see a character manifest a Mark. While it means they’ve achieved the pinnacle of their fighting ability, it also means a short life even if they survive the battle. Power certainly doesn’t come easy in the world of Demon Slayer, but it seems some of the best slayers have decided a Demon Slayer Mark is worth the trade, if it means purging the world of Muzan and his monsters.