Itachi Shinden mentioned that Uchiha Izumi's mother was Uchiha Mizuki, and her father was a civilian Shinobi.
Because Mizuki married a civilian, Izumi's family could not live in the Uchiha Clan's compound and were required to leave the Uchiha.
During the Nine-Tails's attack on the Village, Izumi's father sacrificed himself to protect her, causing Izumi to awaken the Sharingan.
To prevent the bloodline from leaking out, the Uchiha Clan allowed Mizuki and Izumi to return to the Uchiha Clan and rejoin the family tree.
The Uchiha Clan is an extremely xenophobic clan; don't expect these arrogant people to sympathize with the hardships of those at the bottom.
They cannot change their arrogance; even without the two culprits, Danzo and Obito, and that "filial son" Itachi...
...the Uchiha would still have been destroyed.
Weakness and ignorance are not barriers to survival, but arrogance is!
Kagami sighed, "I hope this war can help improve the relationship between the Uchiha and the Village!"
Torifu said, "Actually, there's another reason why the Uchiha are so far away: the public opinion of the Shinobi Allied Forces. People from other Villages say that Madara and Ryou are members of the Uchiha Clan."
"Their resurrection and defection are inextricably linked to the Uchiha, so the Uchiha stayed away from everyone to avoid suspicion."
Kagami nodded and then entered the Uchiha Clan's encampment after Torifu's negotiation with the Uchiha Shinobi.
They went to the place where Shisui was training.
At this time, Shisui was teaching Ninjutsu to a bald child.
Kagami wondered, "Why has a child come to the battlefield too?"
Torifu said, "That's Itachi, the son of the current Police Force chief, Uchiha Fugaku. Uchiha Fugaku brought him to the battlefield in the name of the clan."
"Fugaku? Is he Meiteru's child? Which number chief of the Police Force is he?"
Kagami asked.
Since the founding of Konoha, the Uchiha have had no concept of a Clan Head; outsiders refer to the Uchiha leader as the Captain of the Police Force.
Madara was the last Clan Head of the Uchiha; since him, the Uchiha have never dared to bear the weight of the title 'Clan Head' again.
Torifu replied, "The third."
Kagami lamented, "The third... I really hope the Uchiha can hold the position for a few more terms."
Kagami then looked at his grandson—Uchiha Shisui.
Shisui's hair was very similar to Kagami's, with neat black spiky hair that was slightly curly.
He was the typical handsome Uchiha youth.
At this moment, Shisui was teaching Itachi the Crow Clone Technique.
Kagami looked at Shisui as if looking at his younger self, then he asked, "By the way, where is Munenori?"
Kagami thought of his son—Uchiha Munenori, who was also Shisui's father.
Torifu sighed, "Munenori lost a leg in a previous great war and has been bedridden ever since; his wife has been taking care of him."
"Shisui is very sensible; he became a Shinobi early on to take missions and support the family!"
Shisui does have parents; they just weren't mentioned in the original work, but they were mentioned in the official novels.
Many characters in the original work have living parents; just because the official material didn't design them doesn't mean they don't exist.
For example, the Senju Clan—there's no relevant introduction in the plot, but just because no characters appeared doesn't mean they were wiped out or abandoned their surname.
Just because many things don't appear directly doesn't mean they don't exist.
For instance, Jiraiya's parents are still alive.
Since Jiraiya is only in his 30s now, his parents are old, not dead.
Having no Shinobi talent, they were only responsible for passing the Mount Myōboku scroll to Jiraiya, then living in the Village as ordinary people.
Occasionally, they urge Jiraiya to get married and have children.
People like Ebisu, Genma, Yūgao, and Hayate all have parents, aunts, and uncles.
No one is truly without any connection to this world.
For example, Orochimaru's parents are gone, but he must have relatives, right?
And Obito, it's impossible for him to only have parents and a grandmother in the Uchiha Clan; even if the direct line is gone, there are still collateral branches.
Aunts, uncles, cousins, and so on.
Perhaps when Obito wiped out the Uchiha Clan Police Force, he killed an uncle.
Ryou still has collateral relatives in the Uchiha Clan; his parents are gone, but those parental connections couldn't have been completely severed just because they died.
The Uchiha Clan is a family with one surname and one bloodline; everyone in the clan can trace their relationship through blood.
Even if there's no relation, one can force a connection.
For instance, with an enemy, you could force a connection by saying—I am your non-biological father.
A person is the sum of their social relations; a person is not an isolated individual. Who are you? That is determined by your relationships with others.
Parents, relatives, friends, lovers, masters and disciples, fellow villagers, compatriots...
All these relationships interwoven together constitute the complete—you.
So-called absolute loneliness is having no relationships, making it impossible to form the true you.
Even a hostile relationship allows you to find a part of your anchor in society.
If there isn't even a hostile relationship, that is true loneliness!
Back to the topic.
Kagami sighed as he looked at Shisui, who had shouldered the family burden at such a young age, "It is a father's sorrow to be unable to give a child a complete childhood."
"I am also a sorrow, having given Munenori a broken childhood."
Torifu comforted him, "Kagami, everything will get better!"
Kagami nodded and clenched his fist, "No matter what, we must stop Lord Madara's Eye of the Moon Plan this time!"
Madara's Eye of the Moon Plan would provide a beautiful world for a disabled person like Munenori, but it would negate Shisui's motivation to improve.
Kagami felt that Madara's Eye of the Moon Plan was somewhat beautiful, but also a bit too extreme.
For example, those who have lost the ability to survive and are in despair about the world could be allowed to enter a world of Genjutsu.
But you cannot make everyone enter a world of Genjutsu.
It's fine if you want to 'lie flat,' but you can't demand that everyone else lie flat with you.
It's fine if you don't get married, but you shouldn't go around promoting it so that everyone else stays single with you.
Some things are like masturbation; it's fine to do it in private, but you shouldn't insist on doing it in public.
Isn't that just being a clown?
Itachi formed hand seals and performed Shisui's Crow Clone Technique.
Shisui smiled, "Itachi, your talent is even higher than mine; you've already learned the Bird Clone Technique!"
Itachi was somewhat happy, "Now I can go see my uncle, right?"
Shisui shook his head, "No, how can you deal with Ryou-senpai with those meager skills?"
"Itachi, remember! When the time comes, you must stay close to my side. I will protect you!"
Itachi nodded.
"Who's there?!"
Suddenly, Shisui drew his Shinobi blade and looked warily toward the direction where Kagami and Torifu were hidden.
He sensed two Chakras spying on them, thanks to the Chakra Sensing Technique Minato had taught him after he went blind previously.
Because the Uchiha camp was on the edge of the military encampment, it was very vulnerable to enemy sneak attacks.
Thus, Shisui was very vigilant, occasionally releasing sensing techniques to detect any movement in the surroundings.
He had just performed a sensing and detected two Chakras.
One of the Chakras belonged to the Akimichi Clan, but the other was very unfamiliar yet somewhat familiar to Shisui.
Because it was an Uchiha Clan chakra.
"Kagami, it seems we've been discovered. Let's go out!"
"Alright!"
Kagami and Torifu walked out.
"Lord Torifu, why are you...?"
Shisui recognized Akimichi Torifu; this man had cared about Shisui's situation, showing concern as an elder and comrade-in-arms.
Torifu pointed to the black-haired Shinobi with cracks on his face beside him and smiled at Shisui, "Shisui, do you know who this is?"
Shisui looked at Kagami, his pupils suddenly shrinking to pinpoints, and the Shinobi blade in his hand fell to the ground with a clang.
His lips trembled uncontrollably, "Are you... Grandfather?!"
By the time Shisui was born, Kagami had been dead for a long time; they had never met.
But there was a portrait of Kagami at home, and Shisui recognized him.
Kagami smiled warmly at Shisui, "You're called Shisui, right? You really look like I did when I was a child!"