Tobirama didn't refrain from using the Flying Thunder God Technique to retreat with his students because he didn't want to, he simply couldn't anymore due to being poisoned. That was why he was gravely injured in the initial attack.
According to the autopsy report, he later forcibly used the Flying Thunder God Technique to get his students to safety, despite the backlash it would cause. In that condition, naturally, he couldn't get far, nor could he use the technique again.
The backlash, combined with his prior injuries, left him beyond saving. So, he chose to draw the enemy away alone, giving his students a chance to escape.
As for why Hiruzen and the others were so weak, it was because they were poisoned too.
Shin later verified this with Torifu and received confirmation.
Although no one knew how Tobirama and the others were poisoned, the fact that he died at the hands of a bunch of nobodies was already an established truth.
Tsunade was devastated for a long time after learning the truth.
Later, through the analytical ability of his left eye, Shin identified the poison's components and went to great lengths to gather materials and finally managed to produce a batch. The small vial currently in his hand was one that Orochimaru had prepared for Danzō at his request.
However, since he could create the poison, naturally he also made an antidote. So trying to use this poison against him was pure foolishness.
---
Inside the Hokage's office, Hiruzen had been anxious and restless all day. He couldn't concentrate on anything, not even his usual amusement of peeking through the telescope technique felt interesting anymore. He was eager to get rid of Shin, desperately so.
Especially after Danzō presented that poison. Even Hiruzen was stunned and immediately thought success was guaranteed. But just a day after Shin left, a disturbing image surfaced in Hiruzen's mind.
It was a vision of Shin holding that very vial of poison and giving him a strange smile. Ever since the last prediction involving Shin's Mangekyō Sharingan, he had come to believe these visions, despite not knowing why.
Could this plan have really failed?
If it did, what now?
Shin's power... The moment he thought about the day Shin unleashed his Complete Body Susanoo, Hiruzen's heart pounded wildly.
If that guy went berserk, consequences be damned... Even if he couldn't take on all the ninjas in Konoha by himself, he could easily use the Flying Thunder God Technique to kill me.
I've completely made him an enemy!
It's all Danzō's fault,claiming it was foolproof.
If I tell Shin now that this was a misunderstanding, that Danzō acted alone, would he believe me?
No, I need to get Tsunade to calm him down.
Honestly, Hiruzen was quite the schemer, plotting against both Tsunade and Shin, while still hoping she could help stabilize the situation.
Just as he was panicking and trying to figure out his next move, his pupils suddenly shrank, and cold sweat drenched him again like after a nightmare. Because on his desk, without warning, appeared a small glass vial, no bigger than a pinky finger, filled with silver-white powder.
It was the vial... the same one Danzō had shown before, the same one Shin had held in that vision.
It was over.
What now?
A strong sense of impending death surged from the depths of his heart, and his body trembled uncontrollably.
For the next half hour, who knew what Hiruzen felt. To say that every minute felt like a year would be an understatement. However, he waited and waited, but nothing happened.
Just as he finally began to breathe a small sigh of relief, the door to the Hokage's office was suddenly opened roughly, startling him so badly that he jolted and almost launched into an attack.
But in the next moment, Danzō walked in, smug and full of self-satisfaction. Upon seeing Hiruzen's appearance, he too was startled.
"What's with you?"
"Nothing," Hiruzen quickly composed himself, shook his head, and said, "Maybe I'm just tired."
After the door was shut, Danzō sat down on the sofa beside him and asked, "So, when are we starting our next phase?"
He had long had his eyes on the Uchiha clan. Back when Hiruzen had secretly visited Root to have a private discussion, the two of them laid out three strategies.
The first strategy was to send Tsunade and Shin out of the village. Then, in their absence, gradually weaken their influence while simultaneously boosting Hiruzen's own prestige as Hokage.
The second strategy was to get rid of Shin. The method was simple, poison him. Once poisoned, he wouldn't be able to use the Flying Thunder God Technique. That would be their cue to kill him swiftly and decisively.
The third strategy was to take advantage of that opportunity to severely weaken Tsunade's support base, namely the Uchiha clan and what remained of the Senju clan.
Danzō wasn't happy with the first part of the plan. But he didn't object, after all, he had a backup plan.
Hiruzen was always making him the scapegoat anyway.
But this time, he was prepared.
As soon as news of Shin's death broke, the village would be flooded with rumors, and all of them would point directly at Hiruzen. People would start saying all kinds of things.
At that point, he planned to stoke tensions between the Uchiha, the remnants of the Senju, and Hiruzen, pushing them into conflict while he sat back to watch, maneuvering in the shadows and reaping the benefits like a fisherman watching two tigers fight. Then he would secretly eliminate Hiruzen and Tsunade. With Konoha left leaderless, he would rise with a single command and claim the title of Hokage.
And he had no moral qualms about any of it.
Previously, he hadn't been fully confident about eliminating Hiruzen and Tsunade behind the scenes. But now, with the poison Orochimaru had provided in hand, things were different. All he needed to do was secretly mix it into Hiruzen and Tsunade's food or drink at the critical moment, and everything would fall into place.
While Danzō was lost in his ambitious fantasies, imagining himself seated on the Hokage's throne, Hiruzen let out a long sigh, still shaken, and said, "Shin isn't dead. And the seven people we sent after him... they've all completely lost contact."
"What?" Danzō shot to his feet. "That's impossible! We both have experienced that poison. Even Tobirama-sensei couldn't resist it. And the Second Raikage also fell to it. So how the hell did he survive it?"