Behind him, hearing Kagami's agonized scream, Uchiha Rinne whipped her head around, only to witness the horrific sight of his back being consumed by the raging black flames.
"Kagami!" Rinne's cry was a heart-wrenching shriek of sorrow, tears instantly streaming down her face. The sheer agony of the sight acted as a catalyst, her own eyes flaring to life. The three tomoe in her Sharingan spun wildly, blurring into a vortex on the very brink of evolving into the Mangekyo Sharingan.
Sukuna, nestled in her arms, hadn't been startled by the previous explosions, but now, as if sensing his father's agony, he began to wail, his small cries piercing the tense air. His own eyes flashed red, and three tomoe spun into existence within them.
However, in her despair, the distraught Uchiha Rinne didn't notice this at all.
"It's alright, Sukuna... Your father is invincible. I won't die... not until you and your mother are safe!" Hearing the cries of his wife and son, Kagami gritted his teeth against the searing pain, his voice a firm, reassuring rasp.
Through the haze of pain, his own eyes transformed. The standard three tomoe swirled and morphed into a new, intricate pattern—his Mangekyo Sharingan, its evolution complete. The moment he saw Rinne and his son threatened, the despair and anguish had forcibly awakened his Three-Tomoe Sharingan. Now, enduring the torment of Amaterasu's flames, that agony, combined with the unconscious surge of his cursed energy, had pushed the evolution to its final stage, forging his Mangekyo Sharingan in the crucible of pain.
Cursed energy, born from negative emotions, was fundamentally no different from the Yin Release of this world. It was a potent fuel for the Uchiha's eyes, making this accelerated evolution a terrifying, yet logical, conclusion. The abilities of these new eyes had already provided him with a way to resolve the Amaterasu clinging to his body.
Hearing his strained reassurance, however, only caused a sharper pain to lance through Rinne's heart. A burning hatred for Itachi warred with a crushing despair at her own powerlessness. She couldn't help Kagami; she was a burden. This maelstrom of extreme pain and desperate frustration was the final trigger. Her own Sharingan completed its evolution, the pattern shifting into her own unique Mangekyo. Maybe this was due to the exposure from all this cursed energy form both him and sukuna that she awakened it his easily.
Ordinarily, with her innate talent, such a direct leap to the Mangekyo would have been impossible. But her connection with Kagami, and the subtle nourishment from his Pure Yang Holy Body, had enhanced her own potential and life force, allowing for this miraculous, one-step awakening. However, the physical toll of childbirth, combined with the immense strain of awakening the Mangekyo, was too much for her body to bear. The moment the evolution completed, Uchiha Rinne's consciousness faded, and she collapsed.
Uchiha Itachi, who had been watching this scene unfold, was utterly shocked. He was completely floored. To watch Kagami go from having no Sharingan at all to manifesting the Mangekyo in a matter of minutes was something he thought impossible. Seeing Kagami endure the agony of Amaterasu, yet still find the strength to comfort his family, struck a deeply discordant chord within him.
An image of his own parents flashed in his mind, and an indescribable, bitter emotion twisted in his gut. There was a time when he, too, had valued his family above all else. When had that changed? When had he become someone who could raise a hand against his own mother and father? A wave of regret, so powerful it was nauseating, washed over him, bringing with it a profound sense of despair.
However, as soon as he thought of his living younger brother, Sasuke, his expression hardened with resolve once more.
He looked again at Kagami, who was enveloped by Amaterasu, expecting to see him burned to ashes. But the scene that met his eyes made him widen them in disbelief. Kagami, who just moments before had been a figure of charred flesh, now stood completely unharmed. The inextinguishable flames of Amaterasu were gone, vanished without a trace.
"How could this be?" Itachi was astonished, but his mind quickly processed the impossibly. Staring at Kagami's eyes, he asked, "Is it your Mangekyo's ability?"
Though it was a question, he already knew the answer in his heart. Itachi's heart sank. Kagami was fully recovered, while his own chakra was scraped to the very bottom.
Kagami didn't answer immediately. He turned his head, and seeing that Rinne had only fainted, he breathed a quiet sigh of relief. He then turned back to Itachi and replied coldly, "That's right. It is indeed the ability of my Mangekyo Sharingan."
Perhaps it was a reflection of his desperate thoughts during its awakening. His left eye granted him the ability to create infinite distance between himself and any target, which he named Mugen (Infinity). His right eye could do the opposite, collapsing distance to nothing, which he called Shukuchi (Reduced Earth). He had just used Mugen, making the distance between the Amaterasu flames and his body infinite. Robbed of its fuel, the inextinguishable fire had naturally vanished.
His Mugen could function automatically, a passive barrier of infinity, but he wasn't ready for that. Without the Eternal Mangekyo Sharingan, the constant use would lead to blindness. He consciously kept the automatic function dormant. While his cursed energy could reverse physical damage and heal his eyes, he wasn't sure if it could replenish the finite well of ocular power itself. Ocular power wasn't a physical part of the eye that could be regrown. He had no desire to become blind.
Until he found a way to achieve the Eternal Mangekyo Sharingan, it was better not to overuse his abilities. His base power was more than enough. He wouldn't tell Itachi any of this, of course.
Looking at the now powerless Itachi, Kagami raised his right hand towards him and said coldly, "Do you have any last words? If not, then you can die." Once Itachi chose to attack Rinne, his fate was sealed. The only mercy Kagami would offer was a quick end.
Looking at the new Mangekyo Sharingan in Kagami's eyes, Itachi was silent for a moment before letting out a helpless sigh. "After I die, I hope you won't take your anger out on Sasuke. Please."
He still had Tsukuyomi in his arsenal, but facing another Mangekyo user, he had no confidence it would succeed. The same was true for Shisui's Kotoamatsukami. Kagami was on high alert. There would be no second chance to land an ocular jutsu, and Itachi knew it.