This is the real reason why Kokushibo has six demon eyes in Kimetsu no Yaiba.
As Tanjiro and his friends make their way through different areas searching for answers and the cure for nezuko, they are going to have to defeat demons that are going to cross their path. We have already seen several Superior Moons that have confronted the protagonist and the Pillars, and of course, they have shown to have great demonic power. However, none of these enemies compare to Upper Moon One.
Kokushibo would be the most powerful demon after Muzan Kibutsuji, so much so that it is an opponent worthy of the strongest Pillar of the Demon Extermination Corps, Gyomei Himejima. The interesting thing about this villain is that he has an appearance and a way of fighting very different from other demons, especially since it has three pairs of very striking eyes that have been part of it since it made its metamorphosis. If you want to know why does he have so many eyes Next, we are going to explain everything about them.
Who is Kokushibo in Demon Slayer?

Kokushibo was previously a demon slayer in Demon Slayer
Originally, Kokushibo he was a human named Michikatsu Tsugikuni who was part of the Demon Extermination Corps along with his brother Yoriichi Tsukiguni, who is considered to be the creator of the Breath of the Sun and a talented hunting swordsman. Both are descendants of Muichiro Tokito and Yuichiro Tokitobut the relationship between these brothers would not last long because Michikatsu felt hatred and jealousy for Yoriichi.
your negative emotions led him to become a demon, thus acquiring the appearance that we know today and calling himself Kokushibo. This demon had the ability to create the breathing counterpart of his brotherthe “Breath of the Moon”, which would be one of the most powerful so far.
Kokushibo’s 6 eyes in Demon Slayer

The six demon eyes in Demon Slayer
Upon becoming a follower of Muzan, Kokushibo acquired 6 eyes without eyebrows with red sclera and yellow irises, while her skin turned pale and she got some weird details on her face and body. The Upper Moon One would be one of the demons that most have kept their human formdespite having devoured many innocent people for more than four centuries.
One of the skills he has acquired, thanks to the three pairs of eyes it has, are enhanced reflexes. This gives him the ability to react quickly to his opponents’ attacks, as well as to attack them by surprise. Adding his ability to Hunter Mark of “Transparent World”becomes a high-level power, as it activates the extrasensory ability that allows him to know what his enemy’s next move is and know his weak points instantly.
Why does Kokushibo’s sword have eyes?

Kokushibo Flesh Katana
Kokushibo did not put down his Nichirin sword after transforming into a demon, instead he took it upon himself to upgrade the weapon using your own blood, flesh and bones. In this way, he creates a new katana called “Flesh Katana” that improves various characteristics to make it more durable and sharp. along the blade and hilt several eyes are located that have been strategically placed to increase peripheral vision during combat.
Definitely, the six eyes are something representative and powerful of Kokushibobeing a great advantage when it comes to moving and determining the movements of the opponent to make accurate blows.