Choza took his kids near one of the several trees in the courtyard, and showed them the leaf concentration exercise. Naturally, the energy control required to do this exercise besmirched Choji's capabilities, but Chojusen didn't have a problem. If couldn't at least accomplish this exercise, he might as well throw away the "S Rank" attached to his Energy Manipulation Skill; better yet, he could forget about walking through the air.
Choji's result however, was normal, since he wasn't like Chojusen, and had never trained before. Moreover, he didn't have a system or even had the chance to trained from the womb. But Choza didn't know better, he just assumed his second born son was a genius — he was, just not in the way Choza imagined.
Since Chojusen could already perfectly complete the leaf concentration exercise, Choza began teaching him some basic staff arts. He wanted to train Chojusen's body before teaching him Calorie Control — the foundation for most of the Akimichi Clan techniques. If only he knew Chojusen's "untrained" body would put even elite Jonin to shame.
Choza showed Chojusen the basics of wielding a staff, and after Chojusen repeated his movements the system recognized a new skill.
[Host has learned the Skill: Staff Mastery
Staff Mastery (Novice | 0/100): The lowest level of staff art understanding. The more the user practices with the Staff, the faster mastery over the staff increase.]
Choza noticed that Chojusen was not instantly gifted with the staff, as he was with Chakra control so he told his boys that every week, during the weekends, he would check their progress; Choji would improve his chakra control and Chojusen would practice his staff arts. Once their training reached completion for their respective targets, Choza would teach them something new.
Chojusen had the system, so he could visually see what made his skills improve; if he ever made a wrong turn while following the path of the Staff, the skill wouldn't level up. However, Choji wasn't as fortunate and he struggled to keep up with Chojusen's rate of improvement. Since Chojusen loved his little brother, he would help him out from time to time; an action that create another passive skill.
[Host has learned the skill: Teaching
Teaching (Novice | 0/100) A very basic level of sharing knowledge. The user can teach others only the most basic applications of his own techniques. The more the user teaches, the easier it is to teach afterwards, and the more knowledge the user can impart.]
Coincidentally, all the other clan heirs started training at the same time, which meant that Chojusen couldn't spend as much time with his friends… unless they were training together. But, they were all newbies to training and their parents were worried that letting them "train" together would eventually devolve into just playing around. So, training with his friends was a no-go situation.
Except… for Karin. She wasn't a clan heir, and her mother couldn't teacher her ninja training, so Chojusen would occasionally hang out with her. She was still as clingy as ever, but not in a bad way.
...
One day, Chojusen was walking around the streets of the Hidden Leaf Village with Karin. All throughout this hike, Chojusen could tell that Karin was lost in her thoughts, as she had spaced out more than once. Then, out of nowhere, she suddenly asked him "Chojusen, would you mind… training me..." she paused, and quickly realized he might misunderstand her, so she continued "Just the basic stuff! I'm not asking for you to tell me your clan's secrets, I just don't want to be the only one left out while you guys train..." As her voice died out, she dropped her head and looked at the floor; almost afraid to see if Chojusen would accept or reject her.
Chojusen was ignoring these signs and just responded naturally. He said "I'll have to ask my dad, but there shouldn't be a problem. If he agrees, you can just come to our house whenever you want. After all, it's just like you said; everyone is training. We can't play with our friends now, so the next best thing would be to train together!"
Chojusen told Karin that she could come to his house whenever she pleased for two reasons. One, she already spent a ton of time hanging around Chojusen, so most of the Akimichi members already knew she was his friend; there would be no problems for her to be allowed in the Compound.
Two, he was bored out of his mind, just mindlessly repeating staff moves; he would kill to have a training partner for staff arts. He couldn't ask his brother to train with him in staff arts as Choji had yet to finish his own Chakra control training and his father was only there during the weekends to supervise their training.
He could always go back to training with Chakra Beasts, but for weapons, the best way to improve was by fighting other people with the same weapon. Karin would make for a better training dumm… partner and constantly teaching her could also improve his teaching skill.
It was still a weekday, so Chojusen had to wait a couple days before his dad returned, to ask him if he could teach Karin. Once the weekend arrived, Choza agreed to let Karin train with Chojusen in the courtyard. He hadn't taught Chojusen anything he couldn't share with Karin, and Chojusen was already helping his older brother out; there was no reason to not allow him his wish. Besides, training his friend might spark a bit of rivalry and cause his son to train even harder.
With his father's permission, Chojusen went to Karin's house and brought her back to start training immediately. Chojusen started her training just like his father did with him and his brother; he showed her the leaf control exercise and taught her how to complete it.
For an Uzumaki, with ridiculous energy reserves, Karin had insane levels of talent for chakra control; it didn't take her more than three tries to perfect the leaf control exercise. Chojusen only managed to accomplish the leaf exercise in one try, because he had been training his energy control since even before birth. But Karin, was just a regular person, this was her first time training chakra control… ever.
Needless to say, Chojusen was happy he could skip waiting for Karin to finish training with the leaf control exercise. They could start training in staff arts right away!
Chojusen taught Karin all the basic moves of the staff and the two began to spar. At first it was just light sparring with no real threat of injury. But as Karin's skill with the Staff improved, Chojusen also upped the the level of combat. Karin and her mother were the only people that knew a bit about Chojusen's real power, so Chojusen could make Karin an unstoppable training buddy with the Yang Awakening Skill. He could even eliminate her need for sleep, as well as keep her energized enough to never need a break, but that would certainly look sketchy to the other members of the Akimichi Clan; if he did that, the sounds of staffs clashing would never let the rest of his clan members sleep.
Karin would come over to train with Chojusen every day from noon to eight at night. Her rate of improvement was borderline impossible, if you didn't factor in that she never stopped training all throughout that time. However, that rate of improvement was shared with Chojusen as they would cause each other's skill in staff arts to rise. Whenever Chojusen's Staff Mastery skill improved, his overall performance with the Staff would increase, Karin would reach his level and they would train at that level until Chojusen's skill rose again. In this cyclical fashion, the Staff Mastery of these two kids quickly passed several degrees of proficiency which the ninja world kept track of, and soon, both Chojusen and Karin would become Master of the Staff.
These two crazy kids would only tone down the brutality of their training regiment, when the weekend came around and Choza was there to supervise them. Otherwise, it was all fair game and insanity and chaos were what ensued.
Since Chojusen could only train with Karin from noon to eight in the evening, he spent the time before she arrived, helping his brother with his Chakra control. With his Teaching skill constantly rising, Chojusen's lessons became more and more concise and Choji completed the leaf concentration exercise after two weeks of training.
Since Choji graduated from the leaf concentration exercise, he joined his brother and Karin in fighting with Staff arts. Chojusen received another shock when he learned how talented his brother was with regards to mastering the staff. First, Karin with her Chakra control, and now even his brother was talented with the staff? When did the people around him become talented monsters like himself?
It took Chojusen and Karin weeks to get around level 30 of Novice level Staff mastery, but Choji was just as good as them after only three days of sparring.
After the first month of training, Choza saw both his sons fit to start learning Ninjutsu, so he taught them the clan's famous Calorie Control technique. Calorie Control was a technique that allowed its users to convert calories into Chakra. This was the primary reason most, if not all, the Akimichi clansmen looked so "hefty."
As Chojusen learned more about the technique, he guessed it was probably not intended to convert calories into chakra, but calories into physical energy.
Choza told him that the technique was created by the first ancestor of the clan. The Akimichi Clan progenitor used Calorie Control to power a skill not unlike Sage Mode; this "Sage-like skill" allowed him to be an impressive figure even among Kage-level figures. The Akimichi Clan also used Calorie Control to use something they called Butterfly Mode to fight like their ancestor. There were just too many hints that pointed to Calorie Control and Butterfly Mode being connected to Butterfly Sage Mode. However, Chojusen couldn't bring this up now, and just kept his thoughts to himself.
Since he and his brother were learning Calorie Control, the two started a "special diet" to get used to using the skill. Chojusen didn't need Calorie Control as he had more than enough energy to spare, so he just pretended to eat more than usual. Choji however, wasn't restrained and enjoyed this new "training method." He started eating all the time and consequently started gaining weight.
Since Chojusen didn't care much about this technique, he just left his brother to his own devices and continued training with Karin in staff arts.