First, there was the secret medicine known as Hero Water.
As an immortal, Hero Water gave Yura a way to harmlessly unleash a massive amount of the body's chakra. All she needed to do was study exactly what trigger Hero Water used and which part of the body it stimulated to cause such an enormous eruption of chakra.
Its nature was the same as the Eight Inner Gates.
What Yura wanted to master was precisely this method: stimulating and developing her body's potential on her own, without needing Hero Water.
That meant forming a research team, which required obtaining a certain degree of authority. Yura had no time to research, study, earn money, and scour the entire Shinobi World for orphaned test subjects all at once. Orochimaru was still a little too idle.
Thinking of Orochimaru inevitably made her think of Shin-getsu, the hidden agent she had planted in Konoha.
She summoned a small snake, took out a scroll, wrote down her instructions, and then ended the summoning.
After so many days, even a piece of trash should have infiltrated Konoha by now.
Next, she needed Shin-getsu to conduct extensive preliminary reconnaissance in Konoha. As for whether Shin-getsu would be exposed, Yura did not care in the least. She would continue dispatching spies into the five great villages. If they survived, that would mean they had some skill.
That brought up the second method of increasing chakra: the technique Tobirama Senju had developed through extensive human experimentation, using negative emotions to convert chakra.
Namely, the Zero-Tails creation technique.
This research had likely been developed by Tobirama Senju based on his studies of the Uchiha Sharingan.
Uchiha eyes inherently possessed the ability to convert their negative emotions into special chakra. Every awakening and advancement of their eyes brought a tremendous increase