Turning 3 was a huge thing in a clan like the Uchiha.
First of all, since the Uchiha was a very old clan, it had traditions.
Before 3, you only present your child to your close family and if the child survives till the age of 3, you introduce him to the whole clan.
In fact, with the Uchiha being such an old clan, it isn't exactly uniform, Kaguna knew it well because, in his past life as Tobirama, the Senju clan, equally old, was the same.
There are multiple circles in the clan, with the circle becoming increasingly wide, the widest being the clan, even if one could admittedly call Konoha an even larger circle.
First of all, you have the clan, the Uchiha Clan as a whole, comprising of all the people descending from one single ancestor, the founder of the Uchiha family : Uchiha Yuta.
According to some, he isn't the first Uchiha but no source can prove it.
According to Uchiha legends, the Uchiha would be descendants of the Sage of 6 Paths but a lot of Clans have the same claim.
'Hmmm…' thought Kaguna, 'there may be some truth in it according to the alien factor that I discovered as Tobirama and that I called the Elder factor. The sage of 6 Path might be one of these ancient people that the great clans originate from…'
Then the clan is divided into multiple parts according to the purity of the bloodline.
First, you have the Civilian Branch, Uchiha who lack the talent to be ninja.
They are mainly responsible for managing the resources, some have clan caravan, some possess shops, some are responsible for food production, they are essentially feeding the clan when there are hardships. In exchange, they are protected and if their children by chance awaken the talent to be ninjas, they can easily rise up in the clan and obtain the resources that will allow them to rise far above ordinary shinobi : the clan protect their own and they protect it.
Then, you have the Shinobi Branch, Uchiha Clan members who lack the talent to awaken the Sharingan. If you are born in it, you remain there as long as you don't awaken the sharingan. If you awaken it, you can rise further, into the next Branch : the Main Branch.
It is composed of every Uchiha who awakened the Sharingan, within this sub clan, you have the main family, descendants of the clan Chief Izuna the Elder, not Kaguna's body grandfather but one of his ancestors nonetheless. Namely, he's his great great great great great grandfather and is the first guy who managed to awaken the Mangekiou Sharingan after more than two hundred years without it.
After the main family, you have the great families and then you have the Sharingan owners' families. To create a great family, one must have Kage level strength but most of those who do end up being absorbed into the main family through marriage.
Most of the great families specialize in one art in order to improve the clan, they develop new jutsu, new fighting styles according to the branch they specialize in. Sure, it's not necessarily their only shinobi art they can use but even in a clan like the Uchiha one, you can't just learn any jutsu you want, you have to make contributions to the clan, to earn it.
Your close family supports you in any possible way, but the clan only supports you according to the talent you display.
You can even move through the branches according to your talent or lack of talent.
The higher the branch, the higher the advantages, the stronger, the more talented you are, the more resources you obtain.
The goal is to support everyone while maximizing the chances of having talented shinobis since in the great clans, most of the talent comes from the bloodline.
Anyway, before Kaguna was 3, he was only presented to his family cell, meaning his grandparents and their descendants.
Admittedly, he didn't have only one grandma still alive. Izuna died at his previous self hands, his wife, Yona, died in childbirth while giving birth to Kaguna's mother.
They had 2 girls together : Kaguna's aunt and his mom.
The two of them married a pair of brothers : Shoto and Toji, two Uchiha clan members but the sons of a Kage level shinobi of one of the great families of the Uchiha clan : Akainu Uchiha.
He belonged to the branch of the Uchiha clan that specializes in fire jutsus and he awakened a second bloodline, that of a person who married into the fire branch of the Uchiha clan : Magma Release.
Even more so, it wasn't just a kekkai genkai but a kekkai tota : the combination of three chakra natures.
In fact, among the great families, the fire specialist one is the one with the less pure blood : there have been many marriages across its history with non-Uchiha members simply to obtain their bloodline limits to the Uchiha bloodline.
Most of the time, these bloodlines are lost in the Uchiha bloodline but once in a while, an Uchiha possess one of these.
Kaguna felt a little guilty thinking of it : in his past life, he was the one who arranged this life's mother's marriage, hoping that doing so would lessen the bloodline purity of Izuna's descendants while still seeming benevolent.
Luckily, his mother had a very good relationship with his father, Toji, even if he was often out there doing missions. It was a shame because both her and her sister had either quasi Kage or low Kage level strength. With his current level of strength, he couldn't say for sure but experience told him that... Meanwhile both his dad and uncle were at most elite jonin to quasi Kage powerhouses...
And both mom were spending their time raising their kids.
One had to understand that the whole Uchiha clan contained less than ten quasi Kage level and above powerhouses. The two mothers being at home diminished the displayed strength of the clan even more...
And so… Kaguna only living grandmother was Akainu's wife. She was a member of the main family of the Uchiha clan but was a bit of an edge member… given she was the youngest great granddaughter of Izuna the Elder and was thus a cousin on the second degree of Uchiha Tajima, Madara and Izuna's father. Yeah, the same guy whose fight killed both himself and Hashirama and Tobirama's father, thus awakening Madara and Izuna's Mangekiou…
Anyway…
So… Kaguna's cousins on the two sides of the family were the same people : his cousins Saori and Kimi.
Saori was 17 and in love with a guy from one the lesser Great Families of the Uchiha clan : Uchiha Shinto.
Kimi was 16 and also had a brother : Uchiha Shinichi, a guy who, as previously mentioned, was the son of the Uchiha elder Uchiha Kagami.
And so… here was Kaguna, surrounded by his 7 years old sister and his cousins, being presented to the whole clan, a whole clan of former ennemies of his...
And he had to say hello to every single one of them or else his mom would be VERY angry...
Even his often absent father was here, smiling.
Clan chief Hiroto even took him in his arms at some point.
Yeah, it may not be what every Uchiha clan member went through at the age of three because there are a lot of them, but it was what every main family member went through.
For the others, they had a feast, the presentation feast where every 3 years old of the clan was presented to the clan at the same time.
It's during this ceremony that those who haven't awakened their chakra yet have their chakra awakened.
After this ceremony, if they do awaken their chakra, they will each receive Uchiha training.
They will go to the Uchiha clan training course where they will train and learn 6 hours a day, from 6 AM to 1 PM with an hour of rest in between.
It's a mendatory training time where they will learn how to read, how to write, calligraphy, history, geography, mathematics. They will also learn Konoha sign languages, common Konoha codes, but also Uchiha exclusive ones. They will also learn trapping, tracking, common sense on the battlefield, jutsu theory, ...
They will even learn acting, manners, they will learn torture tactics and techniques to resist it.
At the age of 5, every members of the main family and a few other Uchiha will go to the Konoha Academy, most will go the Clan Academy, remaining in the Uchiha clan system and out of the usable Konoha shinobi system.
The shinobis who come from Clan Academies can only mobilized by the village by mobilizing their Clan.
The ones who go through the Konoha Academy can be mobilized according to the village's need, it's one of the problems Tobirama had where he had to bend in his past life : Clans don't want to be wiped out, they send out most of their particularly talented shinobis and their less talented ones but they usually will keep the bulk of their normally talented shinobis to be deployed according to their interests.
It allows them to protect their shinobis.
Or at least that's the official version, in reality : it gives power to the Clans, it's what allows them a say when there is a war.
After a whole day of going from arm to arm, seing women admire his mom for having such a obedient child, listening to war tales of elders he once fought with and essentially seeing nearly 5000 Uchiha clan members, shinobi or civilians, Kaguna was tired, bored out of his mind but mostly thoughtful because of the kindness they had all showed him...
He realised that... the evil Uchiha Clan was truly good to its own...
'No wonder they get so emotional when one of their own dies. They are essentially very emotional human but with their powerful negative emotions enabling them to awaken a bloodline limit that will radicalize their mindset by having them addicted to the emotions they were feeling at the time they awakened their sharingan...
They are just a clan of emotional addicts...
... And I'm now one of them...