Menō

was a "dragon" that was charged with stopping prisoners from escaping the Astronomy Research Institute.

Background
Menō was a dinosaur that lived in the Land of Redaku millions of years ago. He died while he was still a juvenile. After his death, the wetlands common throughout Redaku preserved his remains, eventually becoming fossils. Over the following millennia, the wetlands changed into a vast mountain range, at the peaks of which dinosaur fossils could commonly be found. It was here that Menō's fossils would eventually be dug up, not far from the Astronomy Research Institute.

A few years prior to the events of Sasuke Retsuden, Zansūru, a paleontologist, discovered a way to revive the dead. He came up with the idea of reviving dozens of dinosaurs to be used as an immortal army in the service of Redaku's Prime Minister, a plan he recruited Gigi to help him with. To test the technique, they revived one dinosaur, which they named "Menō". Zansūru was happy with the result, but did not want to revive additional dinosaurs until a sufficient number of fossils could be assembled. Until then, Menō was charged with guarding the Institute, keeping the prisoners incarcerated there in line.

Being immortal, Menō did not need to eat or sleep, enabling him to patrol the Institute all day, every day. He was given instructions to execute any prisoners who tried to escape, publicly and as gruesomely as possible, in order to discourage additional escape attempts. In this task, Menō was incredibly effective, as not even messenger hawks could come and go from the Institute without permission; this permission was represented by a red cloth, ordinarily only in the possession of the Institute's staff. Over time, Menō's efficiency caused the prison guards to become lax in their duties, to the point that they stopped locking prisoners' cells at night, instead depending on fear of Menō to keep the prisoners obedient.

Despite his constant patrols, Menō did occasionally have some time to relax, which he often spent curled beneath an almond tree; Gigi theorized that he liked the smell.

Appearance
Menō is described as "a massive lizard with a bipedal walk, thick leather skin covered with horns, cone-shaped fangs, and sharp claws." His standing height is 80 centimeters, but the actual length of his body is over two meters from head to tail. Zansūru identities Menō as a, presumably a reference to Tyrannosaurus. The manga and anime depict him as resembling a Velociraptor, with a blue stripe running along his sides.

Abilities
A natural predator, Menō is very dangerous in a fight, having incredibly sharp claws and incredibly strong jaws. His legs are likened to springs, allowing him to travel dozens of meters in a single stride. His tail is powerful enough to shatter wood with a mere swing, giving him a third means of attacks if his claws and jaws are blocked. Being relatively small compared to other dinosaurs, he relies on surprise attacks to defeat larger opponents, targeting vulnerable spots like their neck and legs in order to bring them down quickly. Against regular humans, his size is less of an issue, and he can simply attack them without any special tactic. Sasuke Uchiha, a ninja, offers more of a challenge to Menō; although he does a fairly effective job of blocking and dodging Menō's attacks, Menō is too fast for him to outrun without subterfuge.

Menō's claws are laced with poison. It's unclear if this is naturally-occurring, as Sasuke had never heard of such a thing before, and Gigi is later shown to have a vial of the same type of poison that he coats his other weapons with. Regardless of the source, Menō is aware of the poison and takes advantage of it in battle: after doing as little as scratching an opponent with his claws, Menō temporarily retreats, giving the poison time to take effect. The poison quickly starts to shut down a victim's chakra pathway system, eventually culminating with their complete, if temporary, inability to move. Menō doesn't actually need to wait for this to happen, and can instead resume his attacks in the poison's early stages, when his victims become dizzy and experience sluggish movements.

Sasuke Retsuden: The Uchiha Descendants and the Heavenly Stardust
A man recently imprisoned at the Astronomy Research Institute decides to attempt an escape one morning, believing the thick mists will conceal him from Menō. He successfully scales the wall surrounding the Institute and then drops down on the other side, only to find Menō waiting for him there. Menō kills him and drags his body back into the prison. In the novel, a second prisoner, believing Menō is distracted, makes his own escape attempt, but Menō quickly captures and executes him while the rest of the prison watches.

The executions gain the attention of Sasuke Uchiha, who, like the rest of the prisoners, believes that Menō is under the control of Zansūru. Curious about how Menō could be made to constantly patrol the prison, Sasuke seeks him out after nightfall in order to investigate. When he finally locates Menō coming down a hallway, Sasuke activates his Sharingan and tries to capture Menō in a genjutsu. Although Menō briefly stumbles, the genjutsu has no effect on him and he lunges at Sasuke. Sasuke dodges him, throws him into a wall, and tries to use genjutsu again, but the results are the same. Sasuke opts to leave, not wishing to draw attention to his presence by leaving evidence of a fight. He accordingly continues evading and repelling Menō, but Menō is too fast for him to actually escape from. Having no choice, Sasuke creates an ice dagger, which he uses to cut off some of Menō's claws and stab him in the torso. Menō roars in pain and quickly runs off, leaving pools of blood behind him.

Menō's immortal body regenerates his injuries by the following morning, allowing him to carry out his usual patrols as if nothing happened. Sasuke, still believing Menō is a regular animal, is surprised when he sees this, as he'd worried that the injuries he gave to Menō were fatal. Sasuke tries to avoid meeting Menō again when he leaves his cell after dark, procuring a red cloth in an attempt to ward Menō off, but he forfeits the cloth to another prisoner in need. Menō discovers him soon afterwards and attacks. Sasuke repeatedly dodges him, taking this opportunity to closely examine Menō's body and confirm that his wounds from their previous encounter are completely gone. He tries once again to trap Menō in a genjutsu, this time even using his Rinnegan, but there is still no effect.

After repeated attempts, Menō manages to graze Sasuke's cheek with his claws, drawing just enough blood to poison Sasuke. Menō immediately retreats while the poison takes effect and Sasuke, confused by this, readies the sword he's concealed on himself. Just as Sasuke starts to notices he's becoming dizzy, Menō charges back at him to resume his attacks; Sasuke is able to avoid the most lethal strikes, but Menō manages to hit Sasuke with greater regularity. Sasuke notices the rapid deterioration of his body's faculties. When Menō approaches for another attack, Sasuke slashes the floorboards beneath himself, causing him to fall to the floor below. Menō leaps down in pursuit, but Sasuke has already run off and Menō cannot locate his scent. Sasuke is ultimately found and saved by Sakura, who removes the poison from his body.

A few nights later, Gigi notices that Menō is about to walk by his cell; he lies to his cellmates that he managed to learn Menō's seemingly random patrol schedule. Gigi lures Menō close to their cell with a tree branch that Menō likes the smell of and pets Menō's head. Menō doesn't mind this, and Sasuke in fact notices his normally slitted pupils widening from the experience. One of their cellmates, Ganno, joins Gigi in petting Menō, while another, Penjira, attempts the same. As Penjira approaches Menō, however, his toes slightly leave the boundary of the cell, technically meeting the definition of escaping. Gigi pulls Penjira back, just in time to avoid Menō's crushing jaws. In his attempts to attack Penjira, Menō knocks over an oil lantern, which sets him ablaze and causes him to run off in pain.

A few nights later, Zansūru decides to finally assemble the dinosaur army that he's been digging up fossils for. He has Gigi revive the dinosaurs while he takes Menō to confront Sasuke, who he anticipates will try to thwart their plans. When he finds Sasuke, he distracts him in conversation while Menō sneaks up behind him. Sasuke notices in time to dodge, but Zansūru nevertheless departs, entrusting Menō to kill him. Sasuke, who has now figured out that Menō is immortal, decides against attacking him, as Menō would still experience pain from any injuries he received. Because he's encountered a similar technique before, Sasuke tries a different tactic: he changes the tone of his voice and encourages Menō to calm down. He notices the burns Menō received from the lantern haven't fully healed yet, which he inspects cautiously, all the while keeping Menō's fangs and claws at bay with his sword. He applies water to the burns, which he then cools with wind, creating a soothing ice. This causes some of the hostility to fade from Menō's eyes.

Sasuke apologises for cutting him when they first fought, which aggravates Menō once again. He prepares to bite Sasuke, but grows confused when Sasuke doesn't try to escape; after some visible hesitation, Menō does finally bite his arm. Sasuke does not react to this, instead sympathising with Menō for being brought back to life in a body he doesn't have full control of. Sasuke offers to return Menō to the peaceful afterlife he was taken from in exchange for Menō's help. Menō's eyes grow wide with comprehension, prompting Sasuke to try using genjutsu again. It succeeds, and Sasuke transmits some of his chakra into Menō's body in order to secure control. Menō leaps away, leaving Sasuke to wonder if perhaps he failed, but when Menō pounces at him again it is to lick his wounds.

Sasuke and Menō return to the Institute, where the other revived dinosaurs are attacking the prisoners. Sasuke instructs Menō to save as many of the prisoners as he can. Menō finds one prisoner, Ganno, about to be killed by a herd of dinosaurs. Menō attacks one of them, provoking the others into attacking him instead and giving Ganno a chance to escape. Seeing this, Gigi realizes Menō is no longer under his control, at which Zansūru expresses frustration. Outnumbered, Menō struggles against the herd until Sasuke arrives to help; Menō growls happily to see him. Sasuke sarcastically suggests they run away, but Menō refuses. Instead, Sasuke advises that Menō keep his distance from the other dinosaurs, attacking only when he sees an opening.

Their tactic works against the various herbivores, but Menō soon comes up against an adult of his own species. Zansūru believes that Menō, only a juvenile, will stand no chance, but Gigi corrects him: Menō is able to grow stronger using the chakra of whoever controls him, in this case Sasuke. This enables Menō to overpower the adult. Zansūru, increasingly angry, takes control of all of the revived dinosaurs from Gigi and has them all attack Menō and Sasuke. As dinosaurs from all around the Institute start to converge on them, Menō stands in front of Sasuke, ready to defend him. Sasuke offers to deal with the small dinosaurs and asks Menō to focus on the big ones: he as such picks up Menō and throws him onto the back of the Titan, a large dinosaur that Zansūru is riding. When he lands, Menō begins running up the Titan towards Zansūru, but Zansūru takes flight on a flying dinosaur before he can get near.

Sasuke keeps most of the dinosaurs' attention on himself while Menō lures the Titan to a lake near the Institute. When the Titan get close enough, Sasuke instructs him to attack the Titan's leg. Menō complies, cutting its tendons, and then runs away: because of its size, the Titan can't support its weight any longer and collapses into the water, from which it struggles to escape. Zansūru ends up dying in an attempt to free the Titan, causing the revived dinosaurs to revert to their previous instruction of attacking the prisoners. Menō and Sasuke return to the Institute and track down Gigi, eventually finding him in combat with Sakura. When Gigi sees that he is outnumbered, he surrenders.

Gigi explains how he got involved with Zansūru's plan to Sasuke and Sakura. Menō listens as well, making occasional growling sounds, but Gigi is uncertain how much of his story Menō actually understands. Regardless, Gigi is eventually convinced to return the revived dinosaurs, Menō included, to the afterlife. Menō's body gradually dissolves to dust as his soul begins leaving its immortal body. Menō rubs against Sasuke and growls a farewell to him, while Sasuke scratches his chin and wishes him a good rest. His departing soul embraces Sasuke as it vanishes.

Trivia

 * means "agate".

Menô Menō