"So you can use your Mangekyō Sharingan to reach inside, then?" Kazemori Masaki asked Kagami Uchiha.
"I can give it a try. If my guess is right, anyone with a Mangekyō Sharingan should be able to resonate with certain things left inside," Kagami replied, turning his Mangekyō Sharingan toward a particular spot in the cave.
Although the Uchiha Clan lacked Indra's divine powers, they had still inherited some measure of them. The Mangekyō Sharingan was also very close to the level of Indra's Sharingan, granting it some ability to reach into the realm of souls.
Kagami did not know how Indra had opened the door to the Spirit World. As the Uchiha Clan's ancestor, Indra might have possessed unusual abilities unique to his Sharingan. After all, he had inherited the Sage of Six Paths' "sage eye," and he was its first-generation inheritor at that. It was entirely possible that he had abilities his descendants lacked.
Kagami certainly did not possess power like Indra's. But as he had said, Indra's power still lingered here, leaving the rift in an extremely unstable state. With the Mangekyō Sharingan, there was still hope of exploiting that instability to reopen it.
Although Kagami could reopen the rift and use his Mangekyō Sharingan to project his mind inside, he could not move freely there. Only souls without physical bodies could move through that world. Apart from those using the Kato family's Spirit Transformation Technique, only the dead could do so.
Kagami did not know the Spirit Transformation Technique, but if he died, the soul he had honed through his Mangekyō Sharingan would certainly be able to move freely, just like Madara Uchiha, who had always maintained his own mental image within the rift to the Underworld. Kagami did not think he needed to go that far,