If you thought that the two new techniques were the only thing that he accomplished in these 3 years you would be wrong. While he didn't create new techniques, his physical conditioning and his meditation have brought fruits. Thanks to his stronger body, his chakra reserves had increased to mid-chunin. He had also been able to sense natural energy, however, it was somehow elusive and he didn't dare to absorb it for fear of taking in too much at the same time and turning to stone.
The last achievement was getting a feeling of the first two gates of the 8 Gates: the gate of Opening and the gate of Healing. By experimenting with opening it, he got a feeling of the requirements to open them. They were: a strong enough body and good enough chakra control in comparison to one's chakra reserve.
The more chakra you have the more difficult is to open the gates. This made sense: the gates hold 80% of the user's chakra. So, as your chakra reserve increases, the difficulty of opening the gates augments proportionally. Might Duy, Might Guy, and Rock Lee can perform this technique only because they have low chakra reserves.
Fortunately, while Hijiri's chakra reserves are not so low, he has a strong enough body and good enough chakra control to offset that and he can open the first two gates. Hijiri wasn't interested though in the burst power that came from opening the gates since they left you after in a state of weakening.
Instead, he wanted to permanently open them to obtain extra chakra and maybe a minor bust. He had realized that even with his talent and all his training he wouldn't be able to obtain a chakra level comparable to Hashirama.
To do that he tried to control the flow of chakra and adapt to the opening of the gate but without success. He even learned the Mystical Palm technique to heal the tenketsu while it was open but it only resulted in it closing ahead of time.
He only had a last approach remaining before trying to use seals. But the use of seals would be very dangerous since something could easily go wrong. Unfortunately, the last approach wasn't something that he could try right now, so he could only wait.
Days passed and a month later Hijiri was shown how dangerous was this new world he now lived in.
It was a day like the others. Hijiri had finished training and was returning home. It was late evening and Hijiri couldn't help gazing at the starry sky.
(Hijiri): 'I always marvel at the beauty of this starry sky. In my world, with all its pollution, you couldn't have a sight like this one.'
*Splash*
(Hijiri): 'Shit, I step on a puddle. Wait today was sunny, how there was a…'
He couldn't finish his thought when a hand exited from the puddle, clutched his ankle, and picked him up. A hooded man came up from the puddle and with a swift strike to the neck acupoint he put Hijiri unconscious.
(Masked Ninja 1): 'And that is done. Sneaking in the Hyūga camp was a real challenge. But the prizes were worth the hassle: two pure byakugan eyes and a genius of the Hyūga clan. Better to get out of here before they notice that something is amiss.'
Like so, with Hijiri under his arm, he swiftly and carefully exited the camp. Once out he met with two other masked figures and, after a nod, they started tree-jumping into the distance.
(Masked Ninja 2): "Hey, are you sure about keeping the brat alive?"
(Masked Ninja 1): "Don't worry, he will not be a nuisance. I will take care of him. Besides, even without the byakugan, from the information I have gathered, the Hyūga will still pay a price to take him back. He is considered a genius. Ha, genius. A genius not raised in the blood of war is no… Hey, what?"
While the first masked ninja was busy talking, Hijiri had regained consciousness. Once he quietly assessed the situation, he promptly acted. He activated the byakugan and gathered chakra in his forearms. He then stuck and sealed the tenketsu points on the first masked ninja's arm and chest. This was all done in a couple of seconds.
With a shout, the first masked ninja fell from the branch he was on. While Hijiri freed himself and jumped backward a couple of branches.
The other two masked ninjas, bewildered, looked at their fallen comrade and couldn't help to think: 'Luckily you will take care of him'.
Then the second masked ninja started forming hand signs while the third dashed forward while throwing out a bunch of shurikens. Hijiri jumped up above the shurikens and the third masked man, towards the second one.
At this moment the latter had just finished his hand signs: "Water release: Water Bullet"
A torrent of pressurized water was expelled from his mouth. Hijiri answered with: "Eight Trigrams: Vacuum Palm."
The two techniques met each other with an explosion of mist. Hijiri passed through the mist and finished his jump ahead of the second masked ninja. This one took out a kunai and prepared himself for the clash.
At the same time, the third masked ninja also completed his hand signs and launched a bunch of senbon-like projectiles from his mouth: "Waer release: Water Senbons."
With one armed enemy ahead and an incoming jutsu behind, the two enemy ninjas thought the battle would be over. But at the critical moment, Hijiri twisted himself in the air and started spinning while releasing chakra from all his tenketsu. By doing so he created a chakra sphere with a radius of 5 meters. With it, he not only repelled the incoming water jutsu but also ground to death the second masked ninja.
All of this happened in a bunch of seconds. The third masked ninja decided that the gains weren't worth the risks and decisively escaped.
Hijiri released a sigh. This was his first battle experience and, even if short, it had been exhilarating!
The feeling of adrenaline pumping in his veins and the clash against his enemies were deeply etched in his memory.