Well, I think everyone who played Ghostwire: Tokyo has already made observations about some points in the game, such as: why KK hunts Hannya, who is that guy with the blurred face who appears in the photo with KK's friends at the beginning of the game, and why KK seems to care more about Hannya… in this case? Because of the messes he made, right? And everyone knows that KK helps Akito to stop Hannya and her plan to merge the spirit and human worlds.

Well, I think I have a somewhat "correct" answer about this, since even the light novel doesn't explain very well what the rivalry between these two is.

(if you don't know the light novel, just search on YouTube, okay? That will clarify some things I'm going to say or maybe not ;--;).

My answer is: they were friends in the past, (Calm down! This falls into the realm of "maybe," it's not canonical or widely debated; I'm just stating a specific observation of mine.) when Hannya was still a normal man, a happy man with his family; but after his wife, Okina, died, he couldn't accept the pain of losing the person he loved and went crazy, studying the dark arts, and KK?, being his friend, tried to convince him to stop, to try to accept the grief. This made Hannya think that KK was no longer with him, and he didn't want to support his friend in being happy again.

(that's why in a dialogue during the final boss fight, a dialogue between Hannagon/Hannya says: "Why do you want to ruin this?!" and so on, always referring to the death of the family and KK).

So? That's how KK abandoned him, because he certainly didn't want to support something terrible, and that upset Hannya even more, who began to drown in this madness; and then? Erika, fleeing from her own father to join KK's team to stop him, before dying, it's shown in the novel that KK was a paranormal detective (kind of like Constantine ;--;) who was still alive.

(Even though there were literally few or even fewer interactions between KK and Hannya, and even though they acted like strangers… well… you know that friendship you fought over? And when you run into them again, you pretend you don't even see them? That's it.)

He was still hunting monsters and Hannya himself, probably at some point, (which in this case the light novel ends and there are no other parts ;--;) KK was going to fight Hannya personally, and since he didn't win, he tried to leave to recover his strength and devise a new strategy, but then Hannya thought: "I'm not going to lose anyone else" and then tried to capture KK and ended up killing him… separating KK's body from his spirit.

and since the spirit escaped, he made KK's body into a puppet that is his right-hand man in fights. (yes, this is mentioned in the game's wiki). That's why KK's body is with him and why these two have a rivalry.

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Why does the Hannya mask still fascinate artists centuries later?

Unlike many traditional masks, the Hannya isn't simply "evil."

Its power comes from contradiction.

The face is terrifying at first glance—horns, fangs, rage.

But viewed from another angle, it becomes sorrowful.

The mask represents a woman consumed by jealousy and grief until she transforms into a demon, making it one of the most psychologically complex figures in Japanese folklore.

That emotional duality is what keeps artists returning to it.

I've been exploring that idea through a collection of 89 original Hannya mask designs, each emphasizing a different balance of rage, tragedy, elegance, or menace.

(P.S. im greedy, i know... sorry 😅 thanks for the amazing work nonetheless!)

It's ok to be greedy; but yes, you are correct. Hannya will definitely end in six chapters. Watch out what happens to our favorite plaything Aki-kun~ and I hope you be a good boy and cheer me on as well.