For ocular techniques of Amaterasu's level, both Sasuke Uchiha and Rong Uchiha shed bloody tears every time they used them. Susanoo was even worse—use it for any extended period, and every cell in their bodies would ache unbearably----
Obviously, although ninjas as powerful as Rong Uchiha and Sasuke Uchiha had trained for years and possessed sufficiently advanced Chakra quality, it still did not suit the Mangekyō Sharingan's taste. They could only make do with inferior Chakra, desperately piling on quantity to barely meet its quality requirements----
When did Sasuke Uchiha in the manga stop suffering obvious side effects whenever he used Amaterasu, Kagutsuchi, or Susanoo?
After a moment's thought, Wu Yu knew the answer. It was after Sasuke transplanted Itachi Uchiha's eyes and successfully awakened the [Eternal Mangekyō Sharingan].
Experiments involving the exchange of Mangekyō Sharingan to obtain Eternal Eyes had not been absent from the Uchiha Clan's history, but apart from Madara Uchiha, every one of them had failed. The lessons had been painful.
The only two successful cases, Madara Uchiha and Sasuke Uchiha, had both been reincarnations of Indra. Was that really a coincidence?
Indra's Chakra!
Wu Yu understood at once—the Eternal Eyes were simply too advanced. Low-quality Chakra could no longer satisfy their appetite even by making do; only Chakra of Indra's quality could allow them to manifest successfully.
Combining Indra and Asura's Chakra produced Six Paths Chakra, so Indra's Chakra quality was undoubtedly [Half-Step Six Paths Level]!
Wu Yu could not help laughing. "Looks like Shikotsumyaku really isn't as smart as the Sharingan. Normally, the Sharingan needs Yin-Yang Release Chakra to be properly fed and unleash its true power, yet the vast majority of the Uchiha Clan could never provide Yin-Yang Release Chakra----so the Sharingan automatically downgraded itself into forms that had to be unlocked one