Students of history

"Your philosophies aren't fooling anyone anymore, Lord Danzō.  You should have been the one 'showing your guts' to atone. This is where things end."

"On the contrary, I think this is the start of the greatest age."

"That age cannot start with you."

Sai still struggles in the confines of Itachi's genjutsu.

"What a potent illusion. My curse mark is disturbing is chakra flow to break him out of it, he's still bound. This is different from the last time you used Tsukuyomi on me. Right, Itachi?" Orochimaru quickly deduces what befell Sai. Indeed, Tsukuyomi alters the perception of time. The few times Itachi used it, he made a few seconds in reality seem like several days for his target. But this time things are different. Sai doesn't feel the passing of time. It's accelerated to him. By the end of this, he will have experienced only a fraction of a second, while several hours can pass; like sleep. Itachi stays silent on the case, but he's glad the Tsukuyomi variant is working out, as the previous one drains chakra and tires him out considerably. This one feels more like delivering a knock-out blow.

However, the biggest issues - named Orochimaru and Danzō - are still standing. And Itachi must work his way out of this.

"A shame we didn't bring more bodies." Orochimaru hinting at Danzō with a glance about Edo Tensei, before continuing :

"But that's alright. Let's get out first. Wouldn't want to damage a historic landmark, even ruined."

Itachi closes his eyes and calmly heads out, while Orochimaru and Danzō follow. Sai stays inside.

Both Itachi and Orochimaru are students of history, so the former appreciates the gesture, although the snake is far more of an underhanded individual. A little further back, where collateral damage won't reach the old Uzumaki Shrine, the underhanded individual himself begins the hostilities.

[Eight Headed Jutsu (Yamata No Jutsu)]

Orochimaru was swiftly defeated before, so he decided to start out strong and lay out his strongest snake technique right off the bat, ravaging a sizable portion of his surroundings, but still far enough not to damage the shrine.

"A giant eight-headed snake."

"That would be slightly incorrect, my dear Itachi. Creatures evolve. Creatures have always evolved, and it would be a severe understatement to call this current form merely a snake. I have evolved from a snake..." 

He aims one of his eight heads in Itachi's direction mid-sentence.

"... to a Dragon." The gaping mouth opens wide and misses Itachi who gracefully jumps away from the danger zone. But at the limit of its range, its tongue morphs into Orochimaru to continues his chase, by elongating his neck. After covering a longer distance and stopping, his tongue - forming into a sword - elongates itself some more and slices sideways, splitting Itachi in half.

"For someone who calls himself a dragon, you're still pretty primitive and underdeveloped." The upper half of Itachi speaks from the ground.

"All thing start somewhere. You will be a fitting stepping stone." Orochimaru says as his tongue playfully moves around his face.

"Rather than a start, you seem like a continuously failed experiment." Itachi's lower half has turned into another split upper half.

"Defiling life." One half declares

"Defiling others'." The second half follows up, both being in a mirrored position from each other.

Orochimaru's tongue gets out in a forceful manner that feels like a body wrenching vomit. Out of his tongue, Itachi's head forms. Orochimaru summons his Kusanagi blade to cut it away, and retracts his head back to join the other seven. However

"When are you going to stop?" One of the seven heads' eyes turn into Sharingans, then gradually takes facial features akin to Itachi's.

"You've failed your comrades." A second head morphs similarly.

You've failed your village." And a third.

"You've failed your teacher." A fourth.

"You continue to push your failures onto other people's lives." A fifth.

"Your Genjutsus are still as unsavory as ever." 

"Same goes to your ways."

Orochimaru claps his hands inside one of his eight-headed serpent's mouths and infuses a sizable amount of Sage Chakra, forcefully blowing off the illusion.

"My ways, huh... hahahaha. Itachi, how can you speak of 'ways'..." Four heads crash at Itachi's location.

"...after what you've done to your own clan." Orochimaru reminds him of his sins.

Touché, Itachi remains silent, not even glancing Danzō's way; the latter being the main factor for it.

"That... And I've noticed something."

Itachi's instinct tells him a certain something...

[Fire Style : Fireball Jutsu (Katon : Gōkyakyū no Jutsu)]

... and launches a textbook Uchiha Jutsu on Orochimaru before he could finish his sentence. The latter however is thrilled. Thrilled he can finally use his jutsus again, he decides to go with one that reminds him of older, simpler days.

[Water Style : Water Wall Jutsu (Suiton : Suijinheki)]

'I've mastered all jutsu elements. It's been so long since I've done this.' Orochimaru internally monologues, reminiscing for a split second, while his water wall parries the flaming ball coming his way and both dissipate into smoke and explosion. Blasting a torrent from one of his dragon heads would have been easier but he did it for the sake of nostalgia, as well as a celebration for the return of his arms.

[Amaterasu]

Two of the giant snake heads catch fire. Black fire.

"Susano'o at last. So that's what yours looks like." Danzō remains a spectator, watching the fight unfold, as intel on Itachi's current abilities is far more important than fighting him right now.

Itachi's Susano'o cuts another two using its giant flaming sword.

[Amaterasu]

Itachi's bleeding eye sends another wave of black flames in Orochimaru's direction.

[Summoning Jutsu : Rashōmon Gate]

The snake inside the dragon's mouth summons the gigantic demonic gate to parry the inextinguishable fire.

Cough. The drawbacks are starting to accumulate on Itachi's frail body, and he starts to puke blood.

In the meantime, the Amaterasu's blaze extended to another one of the dragon's heads. As three were being consumed by the dark inferno, Orochimaru was forced to cut them off, or rather detach from them as easily as he would shed skin. The big gate is consumed and weakened, then crashes. He then bursts into a fit of laughter.

"Hahahaha... so my theory was true..." he declares, awaiting an answer from Itachi who remains silent. Orochimaru follows :

"You can't damage this body. You're afraid of harming your brother, aren't you? How endearing."

Two dragon-snake assault Itachi behind his Susano'o only to be repelled effortlessly. They try to squeeze the life out of it, before failing again.

Itachi's Susano'o cuts another one's head off, leaving two.

Out of one, the Kusanagi sword is thrown from Orochimaru's mouth at a dangerous speed. Out of the other, the tongue splits into three smaller snakes, throwing Fire, Wind, and Lightning Jutsu. 

[Yata mirror]

  "All your attacks are meaningless." 

Just as Itachi said, he's impervious to physical and jutsu based attacks, and one more dragon-snake head gets sliced off. Alas, as fate would have it, continuously using his chakra and Visual Prowess (Dōjustus) is taking a toll on him, and his body is starting to falter, coughing more and more blood. The jutsus had no effect, but disease did. Meanwhile, the Kusanagi sword comes back to Orochimaru as he congratulates Itachi :

"Tsk. The Yata Mirror. You really are a good student of history for finding it, I must praise you for that, but you're at your limit, and Danzō didn't even fight yet. What are you going to do, when you can't finish me in your little brother's body?"

Just as he said that, Itachi's Susano'o impales the main body in the dragon's mouth.

"Come on, now. Do you really think an attack of this caliber will ta-"

Orochimaru couldn't finish his sentence before realizing a brutal fact.

"Tostuka's blade ?"

"This kid had Totsuka's blade all along? Crafty one. I can't let things end here, though." 

Danzō approaches. He finally makes his move.