As the learning progress of each spell approached 100%, advancement became increasingly difficult. And since the two Horcruxes had yet to reach maturity, Soji, the top student, had repeatedly "failed to advance" over the past two years, never managing to pass the OLS exam...
But that did not mean he had failed to unlock any new spells during that time!
—Following the formal meeting with Black Zetsu, as well as their brief but immensely rewarding clash, Headmaster Yamada had made tremendous progress in constructing his new energy system.
The convenience of feeling his way across the river by touching Kaguya allowed the magic system to mature rapidly over those two years. As a result, Soji was now able to draw inferences from one instance to another and swiftly expand his repertoire of skills!
For example, he could now fully recreate basic techniques such as the Three Body Technique, water walking, and wall climbing—which had gradually become unusable as the purity of his magic increased—using magic as their foundation.
For another, based on the mature spells he had already acquired, Headmaster Yamada extracted the "code" for editing souls from Horcrux Creation Essentials, then used it as a basis to develop hand-crafted versions of spells like Legilimency and Obliviate!
Granted, compared to the cheat-like abilities directly provided by the system, the latter had not been inscribed onto the skill panel. They were not only more complicated to activate, but their actual combat effects were often unpredictable as well... But in the end, those shortcomings were merely matters of proficiency.
Having achieved the historic breakthrough from zero to one, Soji's plan to replace Kaguya and completely erase her mark was officially underway!
And Uchiha Fugaku naturally became an important test subject for verifying the effects of these new skills.
...As mentioned before, if