Jujutsu Kaisen: Who Is Sadatsuna Ashiya & Why Is He Important?

Jujutsu Kaisen: Who Is Sadatsuna Ashiya & Why Is He Important?

Akutami has not provided us with many details and insights into the history of the jujutsu society, which is why we have very little to work with in general when it comes to things from the series’ past. In the most recent episode of the anime series, Kokichi Muta mentioned the name of Sadatsuna Ashiya, a jujutsu sorcerer from the Heian Era. In this article, we will talk about Sadatsuna Ashiya, as you will find out everything that is known about him in the series.

Sadatsuna Ashiya is an old jujutsu sorcerer from the Heian Era. Nothing is known about him save for the fact that he lived in the Heian Era, that he was a skilled jujutsu sorcerer, and that he is credited as the creator of the Simple Domain, which he actually created to save his followers from cursed spirits and evil sorcerers. A Simple Domain was envisioned as a “domain for the weak,” and it actually helps in many different situations, including against powerful Domain Expansions, as was seen in the series. Sadly, this is all we know about Sadatsuna Ashiya, as Akutami has not revealed anything else about this powerful sorcerer.

The rest of this article will be dedicated to Sadatsuna Ashiya and his story as it happened on the pages of Jujutsu Kaisen. We are actually going to explain who Sadatsuna Ashiya is, why he is such a relevant character, and what his overall contribution to the series’ lore is. We will answer all the important questions about this intriguing sorcerer from the Heian Era, so stick with us if you want to know what happened. This article will contain many major spoilers, so be careful if you haven’t actually read the Jujutsu Kaisen manga, as this article will reveal a lot.

Sadatsuna Ashiya was a powerful Heian Era-sorcerer who is credited with developing Simple Domains

The history of Jujutsu Kaisen is quite rich, and the series has made numerous and various references to historical people and events. Still, sadly, Gege Akutami has not provided us with many details from the series’ history. This is why, for example, we don’t know much about Kenjaku’s and Sukuna’s histories or the past of the important Gojo clan.

There is a lot to discover there, but aside from these main questions, many secondary ones have been raised as well, and Akutami has done little to nothing to provide us with a proper explanation of some of these aspects. One of them is related to a character named Sadatsuna Ashiya, and in this article, we are going to tell you what we know about him.


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During his battle against Mahito, Kokichi Muta, also known as Mechamaru, mentioned the name Sadatsuna Ashiya. Namely, while he was being trapped in Mahito’s Domain, a powerful one at that, he actually spoke of a way to approach that battle since all seemed lost when Mahito managed to trap him and his Mode: Absolute in his Domain. But Mechamaru actually remembered a way to fight this, as he remembered Kasumi Miwa, the girl he was fond of, and her technique – which was called Simple Domain. Now, before we get back to Sadatsuna Ashiya, let us first explain to you what a Simple Domain is.

Simple Domain, whose full name is New Shadow Style: Simple Domain, is a method of countering a Domain. It was created by the founder of the New Shadow School and is mostly utilized by its students.

To shield his followers from the dangers posed by plaguebenders and bad spirits, Sadatsuna Ashiya developed the Simple Domain technique during the Heian era. No one else should have known about this spell outside of the school where it was created. This is why an unbreakable oath was used to forbid his teaching. It is a domain for the weak, allowing them to protect themselves against domain expansion. The Simple Domain approach can still be replicated by seeing it even though it cannot be divulged.

The size of a Basic Domain is merely a few meters. The Simple Domain combats the Domains by focusing on its magic barrier rather than the spells themselves, neutralizing the unstoppable dimension of the linked spells. The Basic Domain only saves a small amount of time when dealing with a real Domain.

Furthermore, the strongest Domains can destroy any Simple Domain that comes into view. Regardless of how “Simple” a spell may be, it will always reach the target with this Domain. Simple Domains can also have rules associated with them to modify the user’s target. The user’s spell does not exhaust after using Basic Domain, in contrast to Domain Expansion. As you can see, this can be quite useful in battle, but it doesn’t work against everyone, and it is not useful in every situation.

So, now that we know what a Simple Domain is, we can get back to the main guy from this article, the guy called Sadatsuna Ashiya. After reading this, you might wonder how Sadatsuna Ashiya, whoever he might be, is connected to Simple Domains? But, believe it or not, there is a very clear and simple explanation for this liaison, as Sadatsuna Ashiya is actually a crucial figure in the history of Simple Domains. Why? Well, allow us to explain.

Namely, Sadatsuna Ashiya was a powerful jujutsu sorcerer who lived in the Heian Era, when cursed spirits and evil jujutsu sorcerers were abundant, which is why many people and weaker sorcerers needed protection. The situation was way more chaotic back then, so different measures had to be taken to save one’s life.


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Sadatsuna Ashiya was powerful, and he also had a group of his followers, probably pupils, whom he had to protect. In order to come up with a way to protect them, he realized that he would have to take into account their weaknesses and the fact that their opponents might be strong.

As Domain Expansions were a thing back there, Sadatsuna Ashiya needed to develop a way for his weak(er) followers to counter powerful Domains expanded by their enemies. And that is how he came up with the Simple Domain, a very special technique dubbed, as we’ve said, a “Domain for the weak.”

So, as you can see, Sadatsuna Ashiya is an exceptionally important figure in the history of the Jujutsu Kaisen lore, as he is the creator of the Simple Domain. This technique has proven useful on more than one occasion. Sadly, save for what we have told you, we know nothing else about Sadatsuna Ashiya, as Akutami hasn’t revealed any additional information, so we can only hope that more information will be revealed.

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