How Sasuke ACTUALLY awakened his Mangekyō Sharingan?
This is a very short summary of Naruto Jinraiden: The Day the Wolf Howled. This novel was written by Akira Higashiyama and illustrated by Masashi Kishimoto. This is the best I could do summarising a 224-page novel in a single blog post. If you want to read the entire thing yourself you can do so here.
End Of Revenge
Sasuke remembers his battle with Itachi: his usage of Kirin and his submission to Orochimaru’s offer of help, and Itachi’s easy defeat of both with his Susanoo. He recalls that Itachi had the upper-hand yet he never followed through with his plan to take Sasuke’s Sharingan. Although it confused Sasuke at the time he was still glad to have finally avenged his clan.
Sasuke dreams of a masked boy who makes him realize that Tobi could have stopped Sasuke’s quest to kill Itachi any number of times. Since he never did, he must have wanted Itachi to die and Sasuke to be consumed with hatred. The boy denies being a dream and claims to lie at the bottom of Sasuke’s consciousness. Sasuke wakes to find Tobi nearby. Tobi offers Itachi’s eye drops to Sasuke to ease some irritation he’s been having. Tobi gives the receipt for the eye drops to Sasuke. Seeing the medicine came from Howling Wolf Village, a former hidden village, Sasuke decides to go there to learn more about Itachi’s fatal illness and if, he was actually ill at all.
The Howling Wolf Village
Sasuke arrives at the Howling Wolf Village a few days later. He learns that the medicine came from a store called Rengyōdō and that it also produces saigenzai, an addictive narcotic. Upon arriving at the store, Sasuke finds that Reishi Kodon and his younger brother Kina Kodon runs the store. Seeing the Uchiha symbol on Sasuke’s back Reishi concludes he must be Itachi’s brother.
Reishi and Kina
Sasuke asks them why they produce a drug like saigenzai. Reishi explains that saigenzai is an erroneously prepared version of their Kotarō, which Itachi used. The Sendō clan is the main supplier of saigenzai, selling it to shinobi that had a hard time adjusting to the unemployment and other harsh realities which came with Howling Wolf Village’s decision to stop being a ninja village for hire. The Sendō clan now wants the secret to Kotarō to increase their profits. Kina also tells him about Rōen, an immortal monster that used to terrorize the village and consume people’s chakra ten years ago. Tenma Kodon, Kina and Reishi’s father defeated it but also lost his life in the act.
One night, Kina arrives at a location where he finds some shinobi under the influence of saigenzai. They beat him up while Sasuke watches from afar. When they try to kill Kina, Sasuke interferes, scaring them off and takes Kina home.
After some discussion of the shinobi system with Sasuke, Reishi admits that his father released Rōen to influence the village’s decision to stop being a ninja village for hire. In the morning, Kina tells Sasuke that the men from the night before were found dead in the same place that Sasuke fought them. As this would make him a murder suspect, Sasuke decides to leave the village. But, before leaving he decides to visit the crime scene along with Kina.
Upon arriving at the scene they find some members of the Sendo clan. When one of them tries to attack Kina, Sasuke scares them off. Soon after they’re gone, Sasuke experiences an intense pain in his eyes. Initially, he thinks it is because of his awakening Mangekyō Sharingan. But the fact that Itachi died a month ago confuses him about what it could really mean.
Abduction of Kina
Before leaving, Sasuke visits Rengyōdō for the last time but fails to find Kina there. Suddenly an arrow bursts through the window with a ransom note attached saying “Kina will be released if they surrender the Kotarō.”
When Sasuke and Reishi arrives at the meeting place, they see some dead Sendō clan members. Reishi follows the scent of the special perfume he uses on Kina to find him. He then applies a special mixture of saigenzai to wipe Kina’s memory. Sasuke realizes that Kina is the murderer, and helps them sneak back to Rengyōdō before anyone finds them.
Reishi explains that the Kodon clan sealed Rōen into their shrine long ago. When his father broke that seal, he controlled it using a special saigenzai. But Rōen broke free during its attack on the village. Reishi’s parents tried to seal it back into the shrine but they failed and as a result, his mother died. His father, unable to do it alone, sealed Rōen into the infant Kina. Reishi explains that when Kina gets angry, Rōen uses his anger to get out. Once it’s released, Reishi has a very short amount of time to suppress it or else Kina will die. Reishi wipes Kina’s memory after each such incident to protect him from the knowledge of what he’s done.
As Reishi finishes his explanation the villagers start to attack Rengyōdō. They believe Reishi and Kina are responsible for the murders. Reishi asks Sasuke to transform into Kina and kill him in front of everyone, making them believe that Kina is innocent and Reishi is the real culprit. Impressed by Reishi’s determination, Sasuke decides to follow through with his plan. Just as he prepares to kill Reishi, enraged Kina emerges from the store to defend his brother and Roen is released.
Sasuke meets Itachi
Recalling that they only have a few minutes to suppress Roen before Kina dies, Sasuke instructs Reishi to hurry up. Reishi uses his special saigenzai to dull Roen’s senses but it recovers quickly. Sasuke uses Kirin on Roen, but it doesn’t work either. Roen captures Sasuke and starts to consume his chakra. As Sasuke cuts free with his Kusanagi he realizes that his Mangekyou Sharingan has finally awakened, giving him the feeling that Itachi is with him.
Sasuke casts a genjutsu with his Mangekyou Sharingan which slows down time and fills the area with crows. Amidst the crows, the masked boy from Sasuke’s dream appears explaining that the seal Reishi is about to perform will last for only seven years and will cost Reishi his life. Sasuke asks what the masked boy wants from him. The boy tells him that he only wants to protect him, and always has. Sasuke realizes that he is Itachi and cannot hold back his tears. Itachi removes his mask and starts to deliver a message before he could finish Reishi completes the seal, the genjutsu breaks and as a result, Itachi disappears.
The Howling Wolf Village hails Kina as a hero. They believe that he sealed Rōen back into the shrine and stopped his murderous elder brother. Due to the saigenzai, Kina didn’t remember much of anything. He asks Sasuke what happened but Sasuke avoids answering his questions.
Shortly after, leaving the Howling Wolf Village Sasuke stands by a beach, reflecting on Tobi’s words about Itachi. As he waits for Jugo, Suigetsu and Karin to arrive he thinks about Itachi some more. Finally as they arrive, Sasuke declares that their team will no longer be Hebi but Taka instead, and their mission from here on out will be to destroy Konoha.
Since this content was released in a novel form, I do not have the actual images of the instances that took place, but these images should give you a pretty good idea too!