how smart was the first six eyes user to even realize how to use his technique

The first Six Eyes user probably wasn’t “smart” in a normal academic sense so much as insanely gifted at reading cursed energy and figuring out patterns fast. In Jujutsu Kaisen , the Six Eyes is described as giving extreme perception and the ability to read cursed techniques in use, which means the user could understand how a technique worked much more quickly than other sorcerers.

Why that matters

The key point is that the Six Eyes does not just help you see more — it gives ultra-precise control over cursed energy and lets the user analyze an opponent’s technique from the flow of energy itself. That would make the first known user seem “genius-level” at reverse-engineering jujutsu, because what looks like intuition is really a broken perception advantage.

How to read that character

So if you’re asking how smart the original user was, the safest take is:

• They were likely exceptionally clever.
• But the Six Eyes itself did a lot of the heavy lifting.
• The real feat was being the first person to recognize how much value that perception had and then actually build a fighting style around it.

In fandom terms

A lot of fans treat the first Six Eyes user as someone who must have been brilliant to “discover” the technique’s uses, but the better explanation is that the ability naturally reveals cursed energy structure so well that the user could figure things out much faster than anyone else. That’s less “inventing genius” and more “having a supernatural shortcut to understanding.”

TL;DR: the first Six Eyes user was probably very intelligent, but the technique itself is what made them look almost impossibly smart.