Demon Slayer Infinity Castle has a character detail hiding in plain sight that makes its villain's backstory even more tragic

Demon Slayer Infinity Castle may have set pulses racing with its (sometimes literally) electric fight scenes, but the record-breaking anime movie also tugs at the heartstrings with the backstory of one of its villains.

As it turns out, however, the Upper Rank demon in question – Akaza – has his tragic past hiding in plain sight, if you know your Japanese history.

Spoilers for the Demon Slayer Infinity Castle ending follow.

Midway through Akaza's fight against series protagonist Tanjiro and Water Hashira Giyu, the narrative dives back into the Upper Three's upbringing, including the moments that bring him into the orbit of martial artists Keizo and his daughter Koyuki – who Akaza (then known as a boy called Hakuji) is engaged to be wed to.

And here's where the hidden detail comes into play. In the present day, Akaza is adorned with a unique series of tattoos that cover his entire body. Those aren't just to look cool.

As pointed out by @imhimgojou on Twitter, those tattoos are in the style of a traditional Japanese pattern known as Kohō no Yuki, translated to 'Snow on a Lonely Peak.' Kohō no Yuki bears a striking resemblance to the name of Koyuki – meaning he has quite literally carried the name of his fiancee on his body since her death at the hands of a rival dojo.

The Easter eggs don't stop there, either: the tattoo on Akaza's torso also resembles the kanji for 'snow' or 'yuki'.

In the English dub, Keizo is voiced by Channing Tatum, who has paid heartwarming tribute to his own daughter.

"Walking the Demon Slayer: Kimetsu No Yaiba Infinity Castle carpet with Evie by my side was honestly a dream come true," Tatum wrote on Twitter. "She's been my anime inspiration from the start, and sharing this moment with her made my first time voicing Keizo extra special… Heart is full and fanboy levels are off the charts!"

Demon Slayer Infinity Castle, meanwhile, is currently inching towards Mugen Train's $500 million record as the highest-grossing anime movie of all time, currently grossing over $450 million at the worldwide box office with notable countries such as France and Germany still to come. It follows Tanjiro and his Hashira allies as they are drawn into the titular Infinity Castle to do battle in a final showdown with Demon King Muzan Kibutsuji and his Upper Rank demons. Infinity Castle is set to be the first of a trilogy.

For more on Infinity Castle, check out our guides on Demon Slayer Infinity Castle 2 and how to watch Demon Slayer in order.