The Mangekyō was the evolved form of the Sharingan. It usually awakened only when a member of the Uchiha Clan who possessed the Sharingan experienced an intense surge of negative emotion, such as the death of someone closest to them.
After awakening the Mangekyō Sharingan, its wielder would gain tremendous power. Its abilities varied according to the desires deep within the wielder's heart, but using it came with severe side effects, including the risk of blindness.
Word of Shisui Uchiha's death spread in the end. Every capable member of the Uchiha Clan had attended the meeting that night, with only Shisui Uchiha and Uchiha Itachi absent, so some clan members believed Uchiha Itachi had killed Shisui Uchiha.
"Itachi, tell us. Did you kill Shisui?"
That day, Sasuke had just returned home when he saw a crowd of clan members surrounding his older brother. Some even wanted to hit him. How could Sasuke stand for that?
Although he was curious about what had happened to Shisui, this clearly wasn't the time to discuss it. He hurried over, spread his arms, and stood in front of Itachi.
"Don't you bully my big brother!"
When those young Uchiha men saw a little brat actually dare to run out and block their way, they immediately wanted to teach Sasuke a lesson. But before the fist one had raised could fall, Itachi stopped him.
"I had no reason to harm Shisui. He was something of a mentor to me."
Itachi stopped there, but his eyes turned scarlet. His Sharingan fixed on the men before him, as though he would attack them too if they dared to strike.
"Hmph, how can you accuse my big brother without even finding out what happened? He treated Shisui like his own older brother. Why would he ever hurt him?"
After hearing that, the men stopped giving the brothers trouble and left with a snort.
"Hmph, we'll investigate exactly how Shisui died. Itachi, you'd better be telling the truth."
Itachi ignored them and instead looked at Sasuke in surprise. He hadn't expected him to say something like that. His little brother really was growing more sensible.
He gazed into the distance and recalled what Shisui had told him that day.
"Itachi, live on..."
Whenever he thought of that, Itachi couldn't hold back his sorrow and anger. Without his realizing it, the Sharingan in his eyes transformed into pinwheel-shaped Mangekyō Sharingan. But he quickly caught himself and suppressed the grief and fury in his eyes.
He tapped Sasuke's forehead with his index and middle fingers.
"To think Sasuke protected me today."
Sasuke swelled with pride at Itachi's praise, seemingly having already forgotten what he'd just seen. He had witnessed Itachi's Sharingan transform into the Mangekyō Sharingan, but he didn't ask Itachi about any of it. Right now, he was completely lost in Itachi's praise.
"Hahaha, I'm amazing! My big brother just praised me! That smug Naruto actually taught me something useful. Next time we spar, I'll be merciful and go easy on you."
That was right. As a transmigrator, how could Naruto not know about the tragedy of the Uchiha Clan's massacre? At this stage, it was an excellent opportunity for him to get revenge on Obito. As for disrupting Obito's plans, Naruto loved doing that.
So he had laid the groundwork well in advance, encouraging Sasuke to express himself boldly so Itachi would cherish his little brother even more. That would make the plans that followed easier to carry out.
Lying in his room, Sasuke was thinking too.
"That's so strange. Why is my big brother's Sharingan different from a normal one? It looks like a big pinwheel. Forget it, I don't know what it is anyway. Father and my big brother are already asleep by now. I'll just ask that blond Naruto when I get to school tomorrow."
Having made up his mind, Sasuke soon drifted off to sleep.
Little did he know that Itachi was being lectured by Fugaku at that very moment.
"Itachi, are you still unwilling to tell me the truth?"
Itachi opened his mouth but couldn't make a sound. He was deeply conflicted. After Shisui's passing, he felt as though he had lost his anchor and had no idea what to do. He wanted to trust the Third Hokage, but with what had happened to Shisui as a warning, he didn't dare trust him so easily. If he told his father, his father might go straight to war with the village, and then the village would surely suffer irreparable losses.
Looking at his eldest son, who was weighed down with worries, Fugaku sighed helplessly and waved a hand, dismissing him.
The next day, Hiruzen Sarutobi summoned Itachi to the Hokage's office. First, he expressed regret over Shisui Uchiha's death, then encouraged Itachi. Only after spending ages making grand, empty promises did he let Itachi leave.
"Danzo, I know you're listening in. Get out here."
"Monkey, what do you want with me?"
Hiruzen Sarutobi had guessed correctly. That old bastard Danzo really had been eavesdropping. If his office hadn't been on the second floor, he would have suspected Danzo had dug a tunnel into it specifically to listen to him talk.
The moment he saw Danzo emerge, he hurled the pipe in his hand at Danzo's forehead without another word.
With a thunk, the pipe made intimate contact with Danzo's forehead.
"Danzo, is this what you meant by leaving it to you? Driving that child Shisui Uchiha to his death? Danzo, look me in the eye and answer me!"
Hiruzen Sarutobi roared furiously, his robes trembling with his rage.
Danzo wiped the blood from his forehead and gave Hiruzen Sarutobi a cold look.
"Monkey, everything I did was for Konoha."
"For Konoha? Do you know he was Kagami's only descendant? Now that he's dead, Kagami's line has ended!"
"What?"
Danzo hadn't expected Shisui Uchiha to be the last descendant of his good friend Kagami Uchiha, nor had he expected to be the reason Kagami Uchiha's line had ended.
But he, Shimura Danzō, had never regretted a move in his life. Of course, the time he had taken half a step back and lost his chance at becoming Hokage didn't count.
After saying that, Hiruzen Sarutobi looked around for something else to throw at this shameless bastard. But after searching for a while, all he found on his desk was the crystal ball. He had just picked it up to throw at Danzo when Root ninja suddenly burst in.
They surrounded Danzo protectively, brimming with hostility toward Hiruzen himself, giving every impression that they would charge in to kill him if he dared make a move.
"Good, good, very good, Danzo. So this is the Root you command. They even dare to attack me now."
Hiruzen Sarutobi was so enraged by Danzo's actions that, in the end, he could only grit his teeth and issue a threat.
"Danzo, I don't want anything like this happening again. Don't forget, I am the Hokage."
"Hmph, Monkey, I may have done some things wrong, but can you really claim you've made no mistakes? You'll regret this sooner or later."
Itachi had already quickened his pace, yet Danzo still caught up with him.
After forcing Itachi to stop, he looked Uchiha Itachi over, then got straight to the point:
"Uchiha Itachi, you have Shisui's eye, don't you?"