Once the Seed of Doubt had been planted, it would take root and grow within him, irreversible.
At this moment, Shisui had already begun to see Youhu as Izuna Reincarnated. It was the only way to explain the many changes in Youhu.
After pondering for a while, Shisui wanted to win Tiehuo over, so he probed indirectly:
"Tiehuo, don't you think Youhu has changed a lot? He's completely different from how he was a few months ago."
Tiehuo glanced at Shisui and chuckled.
"Of course Lord Youhu would be different after inheriting Izuna's Inheritance. And Izuna's Notes mention that the immense shock experienced while awakening the Mangekyō Sharingan can drastically change the awakener's personality."
"I'm not saying that..."
"What I mean is, Youhu has changed so much that it's like he's become a different person. Even if someone went through a severe shock, it stands to reason that it wouldn't completely change the way they act and behave."
Shisui tried desperately to explain, hoping to voice his suspicion that Youhu was Izuna Reincarnated.
"You have a point..."
Tiehuo nodded in agreement, then seemed to think of something. "But Shisui, have you noticed something else? You're different from how you were as a child, too."
"I remember you were competitive as a child and put the clan's interests first."
"But after a mission away from the village, every ninja on your team was killed. When you returned, your personality had changed completely, and you joined the Third Hokage Faction."
"Could I assume that you were replaced, too? That you're no longer the Original Shisui?"
"Lord Youhu also told me earlier that your Mangekyō Sharingan technique, Kotoamatsukami, can Modify Others' Will. Instead of suspecting Lord Youhu, shouldn't you suspect yourself first?"
"How can you be sure you haven't been controlled by Kotoamatsukami?"