Why was Orochimaru so easily taken out by Itachi in an instant?
First, because of the Living Corpse Reincarnation, Orochimaru's soul is unstable after possessing someone else's body.
The soul of the person he possesses isn't devoured by him, but rather suppressed by his spirit.
This forces Orochimaru to dedicate a portion of his spirit to suppressing the original owner's soul.
Second is the prowess of the Sharingan.
Orochimaru's Genjutsu stats are maxed out; he knows Genjutsu himself, so ordinary Genjutsu doesn't work on him.
However, Genjutsu enhanced by the Sharingan is no ordinary Genjutsu.
At that time, Itachi's eyes were already the Mangekyo Sharingan. While the Demonic Illusion: Shackling Stakes Technique isn't a Mangekyo-level Genjutsu, Itachi's massive dōjutsu power made it stronger than ordinary Genjutsu.
Third is the margin for error.
Being a Shinobi is a profession with a very low margin for error; often, a single oversight can decide the outcome of a battle.
For example, in the original work, Konohamaru Sarutobi defeated Nagato's Naraka Path with a single Rasengan.
Konohamaru Sarutobi's Shinobi stats were far inferior to the Naraka Path's.
Unfortunately, there is no level suppression in the Shinobi World. Ranks like Genin and Jonin are merely professional classifications, not power levels.
Konohamaru Sarutobi caught the Naraka Path in a moment of negligence and was able to crush him.
Orochimaru hadn't fought members of the Uchiha Clan much, so he assumed Itachi's Sharingan was just at the standard Uchiha level.
In the original work, when Orochimaru defected, he terrified Kakashi—who also had a Sharingan—with just a single glance, leading him to underestimate the Uchiha Clan's Sharingan.
Without sufficient precautions, Orochimaru was left helpless after being caught by a single glance.
Orochimaru is an all-rounder, proficient in Ninjutsu, Genjutsu, Taijutsu, Summoning, Cursed Seals, and calling for reinforcements...
But Genjutsu bypasses all of that to attack his spirit directly, which is why he was taken out in an instant.
Faced with Ryou now, Orochimaru's situation was different from the anime.
The current Orochimaru has only transformed his soul into the White Scaled Serpent and has not yet performed the Living Corpse Reincarnation.
Furthermore, because White Zetsu cells were implanted in his body, Orochimaru's physical constitution has been strengthened, and his resistance to Genjutsu has increased.
But Ryou's Sharingan is no ordinary Sharingan either, as it has fused with Madara's cells.
Ryou gained Madara's powerful Yin Release boost, causing his Sharingan to regress to Indra's Sharingan, allowing him to activate Susanoo with just three tomoe.
The Genjutsu he cast was infused with spiritual energy no less than that of a Mangekyo Genjutsu.
While it seemed like he took out Orochimaru in an instant, his Sharingan's visual prowess was actually half-depleted.
While fighting Satori, Tobirama also kept an eye on Orochimaru. Seeing Orochimaru taken out instantly by Ryou's Sharingan, he snapped, "Orochimaru, do you never learn?"
During his previous fight with Ryou, Tobirama had consistently avoided eye contact with Ryou's Sharingan; even when he did look, he was on guard.
Having fought Madara and Izuna his entire life, avoiding eye contact with the Sharingan had become a physical instinct for Tobirama.
But Orochimaru lacked this instinct; when he fought Madara earlier, Madara had no eyes.
Thus, Orochimaru hadn't fully realized that when fighting a Sharingan wielder, one must never make eye contact.
Tobirama threw a Flying Thunder God Kunai toward Orochimaru, shook off Satori, and used the Flying Thunder God to teleport next to Orochimaru.
Ryou shouted, "Old Senju Demon, don't even think about it!"
Ryou formed hand seals: "Wood Release: Smothering Binding Technique!"
Vine-like wood suddenly sprouted from the area where Manda was, instantly binding the snake's body before frantically coiling around it and attacking toward Tobirama and Orochimaru on the snake's head.
"Wood Release?!"
Tobirama's expression darkened. Even though he had already learned from Orochimaru that Ryou possessed Wood Release...
...it was still infuriating to witness his elder brother's power being wielded by Ryou.
This was the power of the Senju Clan; yet, instead of being inherited by the Senju, it had been stolen by their rivals, the Uchiha.
It was like seeing the girl he liked get NTR'd by his enemy.
Tobirama grabbed Orochimaru's shoulder and activated the Flying Thunder God Technique to teleport away from the area.
Before leaving, he barked at Ryou, "Inherently evil Uchiha brat, just you wait. I'll deal with you sooner or later!"
"Old Senju Demon, fleeing in panic, are we? Haha..."
"You brat—"
Tobirama cursed in exasperation and then activated the Flying Thunder God to flee with Orochimaru.
In truth, Tobirama and Orochimaru had come to gauge Ryou's strength.
But Tobirama hadn't expected Orochimaru to be so pathetic, getting taken out by a single glare.
Nevertheless, Tobirama had verified the intelligence provided by Orochimaru.
Orochimaru's intel wasn't faked; currently, only Madara or Hashirama could defeat Ryou.
He can activate Susanoo with his Sharingan, has powerful Genjutsu, possesses Wood Release, and has a Tailed Beast assisting him in using Magnet Release...
He even has a Kage-level Summoned Beast—Satori.
It was true that Tobirama could prevent Satori from reading his thoughts, but Satori's stats were no less than those of a Tailed Beast.
Even without relying on its ability to sense malice or Absolute Evasion, its pure aerial acrobatics alone were enough to give Tobirama a hard time.
Ryou wasn't someone Tobirama and Orochimaru could handle; he'd wait until his elder brother finished his training to teach the boy a lesson.
After Tobirama and Orochimaru left, only Manda remained behind.
At this moment, Manda was under the dual control of Ryou's Sharingan and Wood Release, becoming like meat on a chopping block.
Ryou jumped onto Manda's head with Candy and then controlled it to slither toward the depths of Ryūchi Cave.
Ryou had plans for Manda as well; it would be under his control for the rest of its life.
Ryou extracted a Life Spore from his body and implanted it into Manda's head.
Manda, like Satori, belonged to the wicked sort, so Ryou felt no psychological burden in dealing with such creatures.
Before long, the Genjutsu energy in Manda's cranial nerves was depleted.
Manda regained consciousness and immediately realized its situation, sensing Ryou and Satori on its head.
"Uchiha Ryou?! Where's Orochimaru? Where did he run off to?"
Ryou didn't speak.
Candy told Manda, "Manda, Orochimaru has already sold you out. From now on, you're my master's slave snake."
"What?!"
Manda was furious. "That son of a bitch Orochimaru dared to sell me? He must be tired of living!"
Manda then thought about it: Ryou was powerful and could easily defeat Orochimaru and Tobirama, so this wasn't a bad deal.
It had wanted to switch to a more powerful master for a long time.
Manda said to Ryou with great arrogance, "Uchiha brat, I can be your Summoned Beast, but you must prepare 100 living humans for me every time you call me out."
"Anyway, your Uchiha Clan are all evil-doers. You and Madara are hated by everyone in the Shinobi World; human lives are just consumables to you."
Satori stifled a laugh. It remembered setting similar conditions for Ryou, demanding sacrifices to torture for negative energy.
But at that time, it was electrocuted by Ryou until it almost fell apart; now, it had been trained like a dog by his side.
Satori was looking forward to seeing what kind of torture Manda would endure.
Meeting Satori's expectations, Ryou moved as soon as Manda finished stating its conditions.
"Lightning Release: Chidori Current!"
It sounded as if a thousand birds were chirping from Ryou's body, which was now covered in sharp electrical currents formed from lightning-attribute chakra.
Under Ryou's massive chakra supply, the electricity ravaged Manda's body like a lightning dragon.
"Ahhh——"
Manda immediately began howling from the electric shock.
Ryou even called for Candy and Shukaku to join in the beating.
Candy used Lightning Release, Shukaku squeezed wildly with sand, and Satori took flight, devouring the massive amount of negative emotions generated by Manda's torture.
Manda twitched all over from the torture, its body twisting frantically as its scales clattered against the walls of the Ryūchi Cave.
A sharp, raspy hiss escaped its mouth—a sight that made the large snakes listening from the dark recesses of the cave shudder and flee far away.