He was a part of a team of meisters and weapons (among them Stein and Death Scythe) who were responsible for the annihilation of the Star Clan. He apparently knew White☆Star and saw him as he killed an innocent, devolving his clan into madness and becoming a Kishin. After the annihilation of the clan, it was Sid who took Black☆Star, White☆Star's son, disregarding Stein's advice to either kill or abandon the baby, and raised him at DWMA. As such, he is considered not only Black☆Star's mentor, but flashbacks have shown that they shared a brother/brother or father/son relationship.
Soul Eater NOT!
This section of the article is incomplete and requires more information before it can be considered complete.
At the beginning of an orientation session at the Death Weapon Meister Academy, Sid led a meeting with new N.O.T. students, including Tsugumi Harudori, Anya Hepburn, Meme Tatane, Hao, and Raid, as well as his students from the Intelligence Agency, Akane☆Hoshi and Clay Sizemore, who were undercover as N.O.T. students while secretly bodyguarding Anya. After explaining the general rules of the Academy, he concluded the orientation session and dismissed students. When Sid exited the room with Akane and Clay, he was surprised to find Anya, wielding Tsugumi, dueling Hao, wielding Raid. Although Tsugumi had not perfected her weapon form, Anya easily disabled Hao and Raid, prompting Sid to order Clay to bring Dr. Medusa to see to the injured students.
Sid continued to lead classes for Tsugumi and other N.O.T. students, serving as a knowledgeable mentor. Although strict with Tsugumi because of the inherent danger that an untrained weapon can pose, he was trusted by her. He invited Maka Albarn and Soul Eater to join him for these lessons—although he did perform a Sid Chop on Maka for her overly exuberant interactions with her mentee Tsugumi.
While teaching, Sid also led Akane and Clay in an intelligence mission to learn more about the string of Traitors that had been attacking DWMA students. After Akane and Clay apprehended one such Traitor, Sid gathered more information from a colleague, until he discovered that one of the DWMA prison guards had been possessed by some unknown person and killed that Traitor. Later evidence brought to Sid indicated Shaula Gorgon as the witch possessing these persons.
Later, as summer approached, at a Death City bazaar, Shaula possessed Eternal Feather through her venom-tipped jewelry that almost led to her death. Sid contacted Franken Stein to oversee her medical recovery. After healing Eternal Feather and examining her body for toxins, Stein submitted his information to Sid. Sid asked Stein to return to DWMA, but the physician refused.
Sid continued to research more information about Shaula and her venom, joining his weapon partner Mira Naigus and DWMA investigator Joe Buttataki to question Eternal Feather, but the interview brought little new information.
After more weeks of intelligence gathering, Sid noticed details about the thefts of paperwork and research at the Death Weapon Meister Academy, indicating a potential suspect: Meme Tatane, whose sleepwalking habits were similar to the trance that Shaula's Traitors seemed to have. Sid coordinated a late-night sting at the Academy, drawing the sleepwalking Meme to the location while he posted his DWMA agents at the Academy's exit and snipers across the street on rooftops. Although the sleepwalking, hence possessed, Meme arrived, she was followed by Tsugumi and Anya. As Meme's actions were revealed, Shaula controlled Meme to have her attack her friends and escape the Academy, while Shaula herself possessed Sid's very snipers to attack the entrance guards.
As Meme escaped the Academy, Sid followed her to the Square of Liberty in Death City. He was followed by his agents—but Sid then realized that Shaula had possessed them as well. Confronting the witch herself, Sid could not defeat her before she stabbed him with her venom. Rather than control Sid, however, Shaula said his strong will made him a poor candidate as one of her minions. Therefore, she commanded Meme to remove the replica of the Statue of Liberty based in the Square and stab its torch through Sid's head. The explosive sound of this attack alerted Akane and Clay who arrived along with Tsugumi and Anya to discover what Shaula and Meme had done: they had killed Sid.
Sid's corpse was retrieved by DWMA intelligence agents and brought to Stein's office at Tsugihagi Research Laboratory.
This section of the article is incomplete and requires more information before it can be considered complete.
Some time later, rumors had become rife within DWMA about various strange occurrences, all surrounding a recently deceased teacher. The rumors said that he got the idea of absolute freedom stuck in his head and started attacking students to show them the amount of freedom dying had brought him. These stories pertained to Sid's present circumstances but, due to their unsubstantiated nature, they were largely dismissed, especially by Maka Albarn who believed that Sid wasn't capable of such things. However, Shinigami himself soon personally tasks Maka, Soul Eater, Black☆Star and Tsubaki Nakatsukasa with the collection of the now-zombie Sid's soul.The group proceeds to Hook Cemetery, where Sid's grave is located, and gather around his tombstone. Sid suddenly emerges from beneath the ground, grabbing Maka's left ankle in the process, before trying to impale her with a sharpened stake in his other hand. Soul makes it just in time, separating the pair but provoking Sid to substitute his weapon with his own enormous, cross-shaped gravestone. Despite originally being a knife meister, Sid wields this object to devastating effect and initially overwhelms his opponents. He even goes as far as providing his enemies with constructive advice, while still fighting them. It is only after Sid uses Living End that the tables begin to turn and Black☆Star manages to land a highly damaging blow. After Maka's unsuccessful attempt at a Witch-Hunt and Sid's quick return to underground, it is left to Black☆Star to capture him using Trap☆Star. After much interrogation; culminating in Black Star lifting up Tsubaki's dress, Sid finally admits that it was Dr. Stein who turned him into a zombie.
Stein is targeted next by Maka and Black☆Star's teams, as part of the remainder of their lesson. Sid patiently waits with the students while they conduct this operation, even allowing Tsubaki to attend to Black☆Star, injured during the fight with Stein, without trying to escape. However, it is eventually revealed that the entirety of the previous events had all been a trick, set up by both Shinigami and Dr. Stein to better teach the students. 
For failing to capture any souls in his last extra lesson, even though it was just supplementary, Sid decides to charge Black☆Star with an appropriate punishment. This takes the form of cleaning DWMA's huge library which, of course, Black☆Star isn't overly happy with. However, Sid simply reasons that by not completing such lessons it is unfair on Tsubaki and so if he doesn't like it, he should just change his ways. He then proceeds to leave, promising to check back on him later.
True to his word, Sid returns and is surprised by the sight he is observing, as the library is now completely clean. However, he soon notices Tsubaki who announces that she has only one book left to do. Sid's expression quickly changes to one of pure rage, realizing exactly what the "brat" had done but just as he is about to leave to find Black☆Star, Stein explains that he went looking for the holy sword Excalibur. With both predicting the result of such an action, Sid decides it's best just to go back to grading tests.
Ultimate Written Exam
When the students of DWMA are made to partake in a significant test; Sid fills the role of the "exam proctor" and promptly makes an example of Black☆Star, who is currently hanging beaten and bloody from a nearby wall having stolen the test answers, as a reason for why they shouldn't attempt to cheat. He subsequently explains the rules and pronounces the start of the exam. Sid is so diligent in his duty that he easily notices and punishes Soul's cheating, who had written the answers all over his body. Except for this slight hiccup, the rest of the test goes without incident as far as Sid is concerned.
In one of DWMA's many corridors, Sid and Stein discuss an urgent matter, concerning the possibility of Medusa, the school nurse, being a witch. In order to resolve this issue and acquire the much needed proof, Sid locates and subsequently infiltrates her house where he discovers numerous artifacts with a direct relation to witches. However, upon finding Medusa's diary and deciphering her intended plans, Sid is assaulted by numerous versions of Eruka Frog's Tadpole Bombs.
The Eve's Fight to The Death
After the events of the previous chapter, Sid bursts into the commemoration festival heavily wounded and quickly alerts everyone to "get out of here!" He firstly explains that he managed to survive by diving underground just as the explosion occurred, before informing the others that Medusa's group were patiently waiting for the day Shinigami-sama got out of his mirror and gathered together with the teachers in a single location. It then rapidly develops into a race against time, as Sid attempts to activate Compulsive Burial before Free can use his Spatial Magic: Independent Cube. The contest results with Sid as the victor, using his technique just mere moments before Free completes his own. Sid utters his final words to the group involved with the ability, as the cube is sealed.
With the current circumstances isolating most of DWMA's forces within a single room, Shinigami asks if Sid is alright, he replies yes but is extremely apologetic, just wishing he could have done more. Shinigami manages to convince him that he did the best he could considering, before proceeding to discuss Medusa's use of Soul Protect to deceive them, provoking Sid to unintentionally mention the Kishin. This leaves Shinigami with little option other than to reveal the presence of the Kishin, but when he simply announces "there is a Kishin in DWMA's basement", Sid warns him that that's too short.
Due to the conclusion of the previous battle resulting in Asura's revival, Sid had been tasked in gathering together the Death Scythes, who where spread out around the world. Sid managed to successfully summon 4 out of the 8, but those in charge of Europe and South-west Asia were currently both on a mission, the one in charge of South America only said "gugugu" which prevented any communication, whereas Africa just rejected the invitation.
With Medusa's sudden exposure as a witch and her recent death; Mira Nygus, Sid's partner, adopts the role of interim doctor. While she is currently attending to a paralyzed Maka, Sid enters and comments on how nice she looks in her new uniform, before asking if she had a minute. He silently mutters about new intelligence being received from Azusa Yumi, concealing his mouth as he does so, continuing to say that he can't say anymore with the others present. Both proceed to make their exit, discussing outside the exact details of the operation which requires them to infiltrate an Arachnophobia laboratory and destroy the Demon Tool located inside.In one of the many corridors of the facility, two guards chat casually at their post, when suddenly a knife lands square between the eyes of one of them. Before the other has time to react, Sid drops down from the ceiling and breaks his neck in one simple movement. The two bodies disintegrate and their souls are absorbed into Mira's holster, as Sid informs Yumi of their current progression, to which she replies with detailed instructions and information about their target. Unexpectedly the alarm begins to sound, resulting in Sid uttering "impossible" but Yumi confirms that it was Black☆Star's presence at the front entrance, which caused the situation. Sid uses this opportunity to infiltrate the target room, photograph the Demon Tool in question and set various explosives in the immediate area.
After returning to Yumi's position and observing Black☆Star's crushing defeat at the hands of Mifune, Sid takes the decision to use her weapon form to devastate Mosquito's left torso. He attempts a subsequent shot at Mifune, but the samurai easily parries the blast and moves into their blind spot. This moves Sid to compliment Yumi's accuracy, but question whether Mifune is a normal man to be able to avoid her shot so easily.
Nearing the conclusion of a significant battle between Death the Kid, the Fisher King and a single Mizune, Sid suddenly appears and uses Mira to pierce the Fisher King's eye at range, killing him instantly. Sid then tells Kid that he and DWMA's Africa Branch's Recovery Squad will handle it from here, before being told that the witch managed to escape. However, Sid is unconcerned and instead focuses upon the fact that another demon tool has come into their possession.
In a large scale conflict over the acquisition of Brew, which sees the majority of Arachnophobia confronting DWMA, Sid and his respective squad are tasked with suppressing the opposing force. While Sid is requesting that his squad not lose concentration due to the effects of the island's magnetic field, they suddenly come under ambush from the enemy. Sid deftly avoids a swift sword swing to bury Mira, in her weapon form, deep into the opponent's chest, before grabbing the victim's head and repeatedly stabbing them in mere moments. Yumi, presently residing on Sid's back in her weapon form, brings his attention to their allies below who are on the verge of being annihilated just by Mifune. Sid quickly orders Mira to head to a designated location, before he charges into battle.
Adopting a higher vantage point, Sid takes aim and accurately fires at his intended prey, but Mifune easily deflects and recovers from the shot, proceeding then to quickly close the gap between himself and Sid. Sid blocks the subsequent strike using a concealed wrist protector and skillfully manages to connect with Mifune's arm, acquiring considerable distance from him by tunneling through the soft snow. Mifune gives chase and, while sliding down a steep cliff, Sid turns and fires multiple shots, issuing the challenge "come and get me, samurai".Continuing their thrilling game of cat and mouse, Mifune relentlessly pursues Sid but seemingly growing annoyed at his constant tunneling antics, he kicks numerous swords in Sid's direction. These weapons easily and accurately pierce the ground below yet Sid manages an apparently successful escape, however, in the process he suffered a glancing wound to his abdomen. Never the less, he proceeds onwards towards the rendezvous point.
When Mifune reaches this specified destination, he is subjected to various elements in a trap, concluding in Sid grabbing his feet from below as a large block of wood hurtles towards him. In order to keep his enemy in position, Sid suffers a grievous wound to his shoulder, but he quickly gains revenge on a bloodied Mifune by impaling his arm. The two face-off with other, trading words before preparing to begin their next round of fighting. However, observing DWMA's retreat signal the two see no reason to continue any further.
After returning to the original landing location, Sid orders the treatment of the wounded before tending to even his own injuries, when he is soon informed by Kim and Jacqueline of the current situation. Hearing that the other students and teachers are currently in tremendously dangerous positions, Sid valiantly makes the decision to mount a rescue operation despite his wounds, but at Mira's pleadings, he hurriedly gets them treated.
Sid eventually makes it to the magnetic field and begins to ask about the status of Brew but, seeing Stein on the ground and unable to move, he instead simply offers to carry him on his shoulders.
With the recent circumstances surrounding the failure of the operation to capture Brew, due largely to Stein's unfortunate and seemingly coincidental outburst of madness, it's assumed there is a traitor within DWMA. As a result of this, Sid is questioned by Joe Buttataki in his investigation into the possibility of the presence of a spy.
During the course of this interrogation, Sid reveals that his primary mission types are "assassination" and "infiltration", making him the most suitable and likely candidate to be the traitor but he remains fervent in his denial of the accusations.
There is Someone to Admire
He is shown to be at the meeting concerning the Kishin's location. He and the others learn that the Kishin has been hiding out on the Moon and it also appears that after his recent battle against Noah's group, Sid has had his supposed severed arm repaired or reattached.
Battle on the Moon
He was on the moon and sends Akane and Clay to go inside and to find the Kishin.
Sid came inside to check on Akane and Clay but also encounters the new Noah and Gopher. Akune told him he was using them (Noah and Gopher said the opposite). Even though he is annoyed, he continued on in the cave. As they reach to end of the cave, they found a pitch black pit. Gopher offer to light up the pit, but Sid decline him and drop a flare instead. Asura woke up and released his madness upon everyone, only to find that it was a hallucination. Sid then proves that Asura is there.
Dark Side of the Moon
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