Shinji thought the plan over and over, and the more he did, the more feasible it seemed. Whether it was awakening the Rinnegan or sealing the Ten-Tails—even an immature one—both were extremely risky undertakings. You couldn't just find anyone and expect them to manage it.
In the original timeline, Obito had already proved he was capable of wielding the Rinnegan and sealing the Ten-Tails.
In other words, Obito was one of the exceedingly rare shinobi in the current ninja world with the potential to reach the Six Paths level!
That made sense.
Obito's stubborn, extreme nature made it easy for him to develop the resolve to do whatever it took. Combined with his Uchiha bloodline, it was no surprise he could pull off something like this.
And if the plan succeeded, Shinji would gain not only a new sacrifice, but also a brand-new pair of Rinnegan.
As for whether the method was too sinister and cruel, Shinji didn't care much. Obito had blood on his hands beyond counting. Just planning and participating in the massacre of the entire Uchiha clan was enough to justify killing him ten times over.
If the price of Shinji growing stronger was Obito's life, then as an Uchiha, Shinji felt not the slightest guilt.
"But how do I make it work?"
Shinji furrowed his brow.
Whether it was awakening the Rinnegan, sealing the Ten-Tails, or breaking through to the Six Paths level, all of it required an ironclad will!
So simply turning Obito into a puppet and controlling him with genjutsu or some other method would hardly help him reach the Six Paths level. Obito had to act of his own volition and use his own will to overcome the successive challenges of awakening the Rinnegan and sealing the Ten-Tails.
That was the hard part!