Throughout the summer break, Izayoi spent his days training with Hinata.
Every day, he would first locate Ino Yamanaka, transform into her, then go to the Hyuga compound to invite Hinata out. They would head to an abandoned training field, practicing either tree-walking or taijutsu sparring.
Having gained a real friend and discovered her own confidence, Hinata's progress over the summer was astonishing—not only in ability, but also in her overall demeanor.
Hiashi Hyuga was the first to notice his eldest daughter's change. When he learned she was already working on water-walking, he realized she wasn't just going out to "hang out" or "play around."
Izayoi also picked up on the fact that someone was monitoring him and Hinata in secret. But he didn't bother hiding; instead, he decided to test Hiashi's attitude. On one particular day, Izayoi found a reason for Hinata to watch how he did water-walking. He also showed off the Shadow Clone Jutsu, basic Wind Release, and then thrashed Hinata in a taijutsu match.
The very next day, he once again disguised himself as Ino Yamanaka to invite Hinata out. When he saw Hinata freely emerge from the Hyuga compound, he knew Hiashi's response: The Hyuga head was okay with his daughter training alongside Izayoi.
For these established ninja families, Izayoi's background wasn't any big secret: an orphan from a ninja family with no surname, but by the end of the first year—barely through its three semesters—he could already do tree-walking and water-walking (which aren't even taught at the Academy), plus the Shadow Clone Jutsu and low-level Wind Release. Given that kind of talent and chakra reserves, he was clearly a civilian prodigy of this era. Training with someone like him gave Hinata extra motivation, as evidenced by the way she pushed herself on water-walking and how her demeanor changed.
Though Hiashi had been somewhat disappointed in his eldest, he still hadn't discovered Hanabi's potential, so he hadn't fully given up on Hinata in favor of her younger sister. Seeing how just one friend could spark such a transformation in Hinata probably only pleased him more.
As for busting up their "puppy love," Hiashi didn't appear to consider it for two reasons. One, they were just kids. To him, this was just innocent friendship. Two, in his eyes, a future between them was impossible. The Hyuga Byakugan would never be permitted to leave the clan. Izayoi was, to him, merely a tool for helping Hinata grow. The moment anything changed in their relationship, Hiashi would step in and lay down the harsh reality—unless Izayoi somehow became "super-elite," like the Fourth Hokage Minato Namikaze, in which case that might open some other doors.
Izayoi and Hinata, of course, had no clue about any of that. Seeing that Hiashi wasn't stopping them from hanging out, Izayoi completely relaxed. He taught Hinata the Three Basic Techniques and more chakra-control tricks, while using their taijutsu sparring to try and pop her red-tier talent.
Both made major gains that summer. Hinata managed to master tree-walking and water-walking, and she even picked up the Three Basics. But possibly due to insufficient chakra, she hadn't yet learned the Shadow Clone Jutsu. Meanwhile, her Gentle Fist—particularly the Tenketsu Needle—improved drastically.
Izayoi, who had the "Medical Genius" entry in his profile (his mother in this life was a medical-nin who left behind scrolls of basic medical ninjutsu), used his knowledge for a unique training approach. To trigger Hinata's red-tier entry, he initially held back for a few days so she could adjust, but afterward he absolutely beat her down during their sparring—showing zero mercy. Then he'd heal her up after each session.
By contrast, even though Neji despised Hinata, he never actually hurt her—Hiashi was right there, after all. But Izayoi didn't hold back at all. He just pummeled her, then cheered her up once the match was over. Getting knocked around constantly made Hinata's combat instincts skyrocket, and she began striking back with real determination—channeling chakra directly into Izayoi's body. She got so used to "train-then-heal" that she definitely wouldn't show the same timid mercy she did in the original timeline, where she held back against her younger sister Hanabi, ultimately losing to someone five years her age.
This marked change solidified Hiashi's acceptance of their "secret training sessions."
Izayoi never did manage to acquire the "Princess of the Byakugan" red-tier entry from Hinata by summer's end, but he still leveled up considerably. By sparring with her, he'd managed to "steal" the Hyuga clan's style of precise chakra strikes. After gauging Hiashi's response, Izayoi asked Hinata, for "study purposes," to sneak out a copy of the acupuncture-point diagram and the scroll detailing those strikes. He soon grasped both the human chakra-point layout and the method for shutting down an opponent's chakra flow. He wasn't really interested in the Eight Trigrams Palms style itself, but the idea of sealing an enemy's chakra mid-fight definitely appealed to him.
Even though he didn't pop any red-tier entry, Izayoi still picked up two new entries from Hinata. One was the Blue-tier "Chakra Control," which he already had. At that moment, a system prompt sounded in his head:
[Ding! You have acquired the "Chakra Control (Blue)" talent entry. It overlaps with your existing entry. Would you like to merge or dismantle?]
Izayoi chose to merge. Unfortunately, it did not upgrade to Purple—it stayed Blue. However, Izayoi could clearly sense his control had improved. That's when he finally understood how Sakura, with her Purple-tier chakra control, could surpass not only a Hinata who'd been training in Gentle Fist from childhood, but also Shizune, who'd studied under Tsunade—she mastered advanced medical ninjutsu, the Senju's chakra-boosting, and even S-rank complexity jutsu like the Yin Seal and Byakugou in just three years.
It's the same as having two lines of Otsutsuki blood: even if they're both "Otsutsuki Bloodline," the Hyuga version was leagues below the purer branch on the moon. Blue and Purple are worlds apart, and even merging two Blues still doesn't make a Purple.
Izayoi's other snag was a Purple-tier "Kekkei Genkai: Byakugan." But a kekkei genkai is just that: it gives you the Byakugan, not the special Byakugan purity that Hinata herself possessed. If Izayoi hadn't already had "Kekkei Genkai: Byakugan (Purple)," getting this new one would only give him a basic Byakugan rather than matching Hinata's pure Otsutsuki lineage.
So he chose to dismantle this duplicate entry. While merging it might slightly improve his own Byakugan's purity, it wouldn't help him awaken the Tenseigan. It's no different than merging two Blue chakra-control entries and expecting it to become Purple—it won't happen. The moon's Otsutsuki needed to sacrifice the entire branch family's Byakugan—and maybe some from the main family, too—to forge the giant Tenseigan. Their Byakugan purity was far beyond that of the Hyuga. No telling how many Purple-tier Byakugan merges it'd take to evolve a Tenseigan. Merging just two was obviously a waste.
Dismantling the Purple-tier Byakugan netted Izayoi a large number of points—enough to change his system's status display:
[Host: Izayoi]
[Talent Entries: Otsutsuki Bloodline (Red), Super-Kage Aptitude (Gold), Kekkei Genkai: Byakugan (Purple), All-Attribute Constitution (Purple), Medical Genius (Blue) "+", Chakra Control (Blue) "+"]
[Points: 1791]
He now saw plus signs next to "Medical Genius" and "Chakra Control," indicating both were available for upgrades. That was the purpose of the points system.