Because he also possessed Karma, Soji knew that completing reincarnation through an imperfect vessel would affect one's lifespan.
At best, one could endure for ten days to half a month. At worst, they might only survive for a few hours!
Therefore, if he forced Isshiki to complete his reincarnation using Jigen's imperfect vessel, Soji had basically already won half the battle.
Why only half?
The reason was simple. If Isshiki completed reincarnation through Jigen's body, recovered his peak strength during his limited lifespan, defeated Soji within that time, and found another perfect vessel to imprint with Karma, he could still continue living.
Of course, such conditions were truly harsh for Isshiki.
Even if Isshiki had prepared another perfect vessel, the prerequisite was that he had to defeat Soji first!
Normally, under such circumstances, Soji could simply stall Isshiki to death!
Moreover, the reason Soji had not attacked directly and instead forced Isshiki to complete reincarnation was due to a small selfish desire.
He yearned too desperately for an opponent!
He did not know when it had begun, but Soji had grown accustomed to being invincible.
Yet invincibility was lonely too.
Other than drawing with Madara Uchiha when Madara had briefly recovered seventy percent of his full strength, Soji truly had never again encountered an opponent who could make him feel threatened and force him to go all out.
Even Nagato and Obito joining forces afterward had merely allowed Soji to loosen up a little.
After Soji's life level broke through to the Six Paths level, he had fought Fusion Momoshiki and transformed Urashiki Otsutsuki in succession, but to Soji, they were at most comparable to Nagato and Obito fighting together back then.
They could bring Soji a certain amount of enjoyment, but they clearly could not make him fight without