He hated the cursed energy.
No, that would be the wrong wording. What he truly hated was the being behind cursed energy — not the energy itself. Once you learn about the cursed energy enough and master it thoroughly, just like he did this past millennium, you will learn a few secrets about the cursed energy itself. For instance, cursed energy isn't just mindless power—something is behind it, guiding it.
A kind of cursed spirit, one could say, one that's beyond anything current humanity could face and one that might be as old as humanity itself. Perhaps it is the first cursed spirit that is ever born, or perhaps it is not; who knows but one thing he knew for certain is that it is a being infinitely close to a god. So close it could even direct the fates of those who are gifted with cursed energy, which is basically everyone. Little by little, this thing was guiding the development of the human race itself and perhaps more.
"How annoying."
He hated this feeling of being controlled very much, with the fact that over time humanity might no longer have free will, it just didn't sit well with him. Which is why he decided to do everything in his power to make sure humanity would break free from the grasp of this unknown creature, no matter what.
His hand moved, picking up a red string. He connected the picture of a child with pink hair to a rough sketch of a four-armed humanoid creature. Then a picture of a finger, a young man with white hair, black hair, and a temple. Making evidence boards had become a recent hobby. Not the most efficient way to plot global-scale manipulation—but damn, it was dramatic and satisfying to look at.
Well, somehow the fate between Star Vessel and Six Eyes is broken by the cast-out of the Zennin Clan. Toji - he believes that was his name, was, little abomination born without cursed energy, which is one way to break free from the creature's influence, but not a feasible one at all. Losing the ability to use the cursed energy for a little bit more physical strength isn't a profitable deal in his opinion. Humanity is growth without the use of cursed energy would hit a bottleneck in his opinion, but still, thanks to him, he finally made the breakthrough on his plan.
Tengen, without a vessel to rejuvenate her human body, will have no choice but to evolve into a 'higher' being. One that's fully optimized to use cursed energy, similar to cursed spirits, but still not exactly one. She has ascended into a hybrid that is born without being limited by his own limited imagination, like how the Death Paintings did.
A perfect base to create an ultimate weapon against that Being, one could say. A blank canvas that is just waiting to be drawn upon, the template for humanity is the next evolution.
After fully formulating his plan, he lets out a satisfied sigh. Of course, his plan wasn't perfect; there were rough spots here and there, and a few things he must improvise upon, but still it was a good one, at least better than one he made a decade or two ago. As he was prepared to leave the room, he noticed the mirror hanging on the wall and saw the reflection of his... current body.
"Well, it seems like it's time for me to change my body."
He muttered to himself while looking at himself in the mirror. The body he was currently wielding was a female one, or to be exact, it was the body of a woman named Kaori Itadori, one he used to create Sukuna's vessel. Anyway, he had already found a great body with a cursed technique crucial to his plan.
"But damn, did I put on a weight."
Kenjaku held his, or rather her, stomach and whispered as she squeezed it. Maybe it won't hurt to put this body back into the proper shape before disposing because of respecting the dead and all that stuff. Definitely not because she felt like this flaffy belly of hers poking fun at her.
"I wish I didn't have use for this body."
She glanced at the plan she had carefully formed for a few seconds before looking away. It was a cruel one, one that would potentially doom humanity, and relied too much on the what-ifs and chances, but perhaps only because that fact it was the one with the greatest chance to succeed. And he would make it succeed.
"Tengen, my friend, perhaps this is the last century we will play this millennium-old game of ours. You had your chance and failed, now it's time for humanity to taste father's tough "love"."
With that, she leaves the room, not realizing that once she's done so, the drawing hanging in the middle of the board moves. It was a strange cat-like creature with one eye, first, it blinked before making a hand seal with its three-fingered hands. The red strings shifted. New connections formed. The creature's single eye narrowed as it let out a silent, knowing laugh.