Danzo Shimura is one of Naruto's most wildly controversial characters. Having served Konoha for decades and even operating directly under the second Hokage, Tobirama, he has accumulated much influence and renown in the Leaf Village.
After Pain's attack, the Foundation leader attempted to assume the mantle of Hokage himself. With Tsunade out of commission, this ambition was not only possible, it was looking increasingly likely before Sasuke intervened. There are several reasons for and against the likelihood of Danzo becoming Hokage, and we analyze his past, demeanor, influence, and even abilities to speculate for and against why he could have claimed leadership.
10 Could Have - One Of The Elders
The Village Elders were essential decisionmakers when it came to Konoha's wellbeing. They served as a sort of political "elite" in the absence of Hokage and were even responsible for helping procure their replacement.
Danzo himself was on this council, entailing that he had a considerable amount of influence. Should he have coaxed the other two to nominate him (as they often agreed), it would be incredibly likely that he would find himself as Konoha's appointed figurehead.
9 Couldn't Have - Killing The Messenger Frog
When the village came under attack, a messenger frog from Mt. Myoboku was dispatched to Konoha and was responsible for sending out aid to Naruto. Before he could leave, Danzo assassinated him and belayed the shinobi's return to the Leaf.
Though he was technically able to get away with this, it was only a matter of time before the ninja of the Leaf and the toad sages of Myoboku collaborate to figure out what actually happened to the emissary. Considering that Danzo was the last one seen with him (and the sword marks on his body match that of Danzo's weapon), it would incriminate his guilt.
8 Could Have - Izanagi
Danzo's Izanagi arm intriguingly renders him a capable leader. Though it does not make him any more charismatic, it gives him extra lives in case someone tries to assassinate him.
This evinces that in a time of crisis (such as when Orochimaru attacked Sarutobi Hiruzen), he would be able to endure against his assailants until help had arrived. It would preserve the Leaf's most crucial figurehead in a time they needed it the most ~ even if it would reveal Shimura's dark secret in the process.
7 Couldn't Have - The Anbu
Unlike the Foundation (who were exclusively devoted to Danzo), the Anbu were the servants of the acting Hokage. When Shimura's assassins came for Lord Third, he was willing to forgive the sharingan user's transgression under the condition he not betray him again.
While Sarutobi would take Danzo's treachery to his grave, that does not entail the Anbu who protected them against the Root would forget as well. It's possible that they might lead an operation to take him out permanently, should he go anywhere near the position of authority he desperately craved.
6 Could Have - The Foundation
The Foundation were an elite group of assassins dedicated to enacting Danzo's will exclusively, even above that of the Leaf's. They were conscripted into his service based on their merits, and certain families would be coerced into surrendering their most talented individuals (such as Torune of the Aburame clan).
Not only are they willing to betray Konoha in his name, they are forced to surrender their emotions and inscribed with a rune on their tongue so they cannot possibly hope to betray their master. This makes them the perfect expendable operatives and allows Shimura to assassinate his political opposition with impunity.
5 Couldn't Have - Goal For Naruto
One of Danzo's primary objectives was to keep Naruto locked away, as he understood the tremendous advantage behind being able to harness a Jinchuriki. However, by the time he expressed noticeable interest in the young Uzumaki, he was saving all of Konoha from Nagato's plot.
This proved not only that he was capable of mastering Kurama's power, it made him a charismatic figurehead among the people. If Shimura were to attempt arresting him, it would be a political disaster, and if he attempted to seize him in the night, Kakashi would definitely find out.
4 Could Have - War Hero
One of Danzo's most advantageous qualities is that he is a war hero. He served alongside Sarutobi under Tobirama during their battle against the rivaling nations, spelling that he has fought side by side with two previous Hokage.
This increases his already prestigious status as a village elder. Since Konoha has constantly seen conflict, their tendency to venerate their warriors would work well in Shimura's favor and enhance his public image. If given the chance, he would capitalize on the opportunity it made for him.
3 Couldn't Have - Pact With Orochimaru
Danzo's Izanagi arm was not free. It was made for him by Orochimaru after they had struck a bargain. The two of them are close associates, with one often assisting the endeavors of the other for a symbiotic relationship.
However, the Sannin is a war criminal. If their relationship was discovered, it would spell the end of his term as Hokage and publicly ruin him. Considering that Yamato and Kakashi are both aware of it, it is a huge problem he is unlikely to be able to cover up.
2 Could Have - Five Kage Summit
During the Five Kage summit, Danzo served as the acting representative for the Leaf village. Moreover, he wore the regalia of the Hokage, cementing his position as its leader to the other villages (since Tsunade was unable to attend herself).
Though the Raikage was distrustful of Shimura and his intentions, they both agreed that Sasuke Uchiha was to be disposed of. Because Shimura was able to make such a palpable presence on the world stage, his transition to Konoha's leadership would have been much more seamless than other possible candidates.
1 Couldn't Have - Sasuke
While the Uchiha genocide had been effectively covered up through Danzo's machinations, Sasuke was informed about it through Obito and was even on the cusp of confronting the elder at the Five Kage summit before he fled.
Though he may have been able to protect himself with other shinobi, Shimura's vanguard would prove an insufficient defense against the avenging ninja. Even the Izanagi he wore on his arm would not be enough to compensate for the disparity in their skill, and Sasuke would enact his vengeance for his brother and family regardless of the consequences.