Jokes aside, En had indeed found the real reason.
It was because, after witnessing his death, Ruri did not produce that special Yin-attribute chakra necessary for awakening a Mangekyō.
To verify this theory, En used a shadow clone to assist in performing the eye-transplant surgery between him and Ruri.
Then, using the Yin-attribute chakra stored within his own body, he nurtured Ruri's eyes.
At the same time, he used Transcription Seal to set three automatic activations of Heaven's Reversal, just in case that Yin chakra caused trouble.
The final result of all this effort was the six-petaled snowflake Mangekyō now shimmering in En's eyes.
Ruri asked curiously, "What's the ability of my Mangekyō?"
"That…" En smirked, "why don't you experience it yourself? Your dōjutsu is quite special."
He formed hand seals and created three shadow clones.
"Hmph. Even if you don't tell me, I can already guess a few things."
"Come to the basement. I've prepared the materials long ago."
En's basement was small, but surprisingly well-equipped — enough medical tools to perform minor surgeries.
To prepare for this day, En had spent years studying human anatomy.
He couldn't perform high-level medical ninjutsu, but he could manage a low-end Mystical Palm Technique and handle a simple eye-transplant surgery with ease.
After a series of tedious procedures, Ruri stepped off the operating table. She pulled away the bandages covering her eyes and felt the dōjutsu power flowing within them.
A powerful aura subconsciously radiated from her body… yet something felt different.
Whenever she had activated the Mangekyō before, she could clearly feel its strength—and the burden it placed upon her body. But now, despite her Mangekyō being fully active, she felt none of that heaviness.
Instead, there was a refreshing lightness, like someone recovering from a severe illness.
Ruri picked up a mirror from the table. Reflected back at her were Mangekyō eyes with a complex pattern: three curved droplets linked end-to-end, encircled by a six-petaled snowflake.
She didn't need to be told—she understood immediately.
"This is… the Eternal Mangekyō Sharingan."
En's voice came from the side,
"These were once the very eyes Madara used to fight the First Hokage. How does it feel, Ruri?"
A flicker of displeasure crossed her gaze.
"I told you, didn't I? I never needed you to give me your eyes."
En chuckled softly, lifting his hand as if to pat her head—but hesitated, and lowered it again.
"I no longer have any reason to keep these eyes. But you're different, Ruri. You still have people you want to protect. So take them. This is the only gift an unqualified father like me can give."
His sudden display of fatherly affection left Ruri momentarily at a loss.
"I never said you were unqualified. Don't assume things." She turned her head awkwardly, speaking quietly.
It was the truth. She had never thought En was a bad father.
If anything, if he acted like a normal parent — hovering around her, fussing over her every day—she'd probably feel even more uncomfortable.
Hearing her words, En let out a relieved smile.
"Right, about your Mangekyō ability. You should know it now, right?"
Ruri nodded slightly.
Just as he said—it was special, and explaining it aloud would be troublesome. Experiencing it was easier.
Her dōjutsu was called Ancient Echo of Heaven.
The right eye allowed communication with her past self. At first glance, it seemed unimpressive—but if used cleverly, she could theoretically communicate with her future self via indirect means, thereby achieving a form of future prediction.
For example, she could leave information somewhere that would remain for decades. Her future self could then receive it and relay the necessary message to her current self using Ancient Echo of Heaven.
But the ability had limitations: she couldn't precisely target the time the message arrived, nor was message integrity guaranteed.
A few missing words could twist the meaning entirely. So careful phrasing was essential.
In contrast, her left eye's ability was far simpler — and more brutal.
It allowed her to summon her past self as a true physical entity.
However, the closer in time the target was, the fewer selves could be summoned.
If that was all, it would simply be a high-end shadow clone technique.
But the ability came with a unique shadow dimension—a space where she could store her summoned selves.
Not only that, she or others could physically enter the shadow dimension, and it connected through the shadows of her other selves.
It was essentially a "youth version Kamui Dimension".
Shame Mitsuki wasn't here — he would definitely complain that this father-and-daughter duo had the most ridiculously cheat-like Mangekyō abilities in existence.
Ruri's left Mangekyō began to rotate slowly.
Her shadow suddenly expanded at high speed, and a girl identical to her stepped out from it.
With a light leap, the version of Ruri from earlier — the one who had just entered the basement before the surgery — walked out from the shadow space into reality.
Past Ruri looked around curiously. "So this is my Mangekyō ability?"
Ruri shot her a glance.
"My Mangekyō ability. You're just a replica."
"Is there a difference? Past me is still you."
Ruri didn't want to debate philosophy with herself. She snapped her fingers and sent the replica back into cold storage in the shadow dimension.
"By the way," En asked, "you should still be able to use my Mangekyō ability, right?"
"Mhm. I can use it, but controlling it isn't as easy as before."
Ruri tested Ancient Echo of Heaven and found its temporal precision had decreased.
But she now had an endless supply of ocular power. A bit of practice would fix it.
Staring at her Eternal Mangekyō in the mirror, feeling the overwhelming, surging dōjutsu power flowing through her, Ruri felt terrifyingly strong.
"Right now… haven't I already surpassed him?"