Underground beneath Naka Shrine.
Sasuke stood in a vast circular chamber.
The walls were covered in densely packed Cursed Marks, and a complex array had been drawn across the floor.
"This is where the Clan Heads of the Uchiha Clan trained their Mangekyō Sharingan throughout the generations," Shikamaru explained. "These Cursed Marks can stabilize ocular power and prevent the side effects of the Mangekyō."
"Would they work for the Rinnegan?"
"They should," Shikamaru said. "The Rinnegan is an evolved form of the Sharingan. At its core, it's still the same kind of power."
Sasuke nodded and walked to the center of the chamber.
"How do you plan to train?" Shikamaru asked.
"I'm going to try a new Dojutsu," Sasuke said. "One I've never dared to use before."
"What technique?"
"Heavenly Realm."
Shikamaru froze.
"Isn't that Kaguya's technique?"
"Yes," Sasuke said. "But the Rinnegan and Kaguya's Rinne Sharingan share a Common Origin. In theory, I should be able to use that technique too."
"In theory?" Shikamaru frowned. "You've never tried?"
"No," Sasuke admitted. "The technique consumes too much Chakra, and it requires an extremely deep understanding of space."
"Then why risk it now?"
"Because if I can master Heavenly Realm, we'll have a much better chance against Isshiki." Sasuke looked at Shikamaru. "Isshiki can definitely use space-time ninjutsu. If he has the advantage over us in that regard, we won't stand a chance."
Shikamaru fell silent for a few seconds.
"Fine," he said. "I'll keep watch outside. If anything goes wrong, call me right away."
"Yeah."
Shikamaru left the training chamber.
Sasuke took a deep breath and closed his eyes.
His consciousness sank into the depths of his Rinnegan, sensing the immense ocular power within.
Toneri's Tenseigan Chakra still flowed through his body like a green river, nourishing his damaged ocular