Clay tries to present himself as a capable EAT Central Intelligence member. In his leisure time, his nervousness and clumsiness betray that calm demeanor. But in combat, he shares with Akane a largely cool-headed demeanor, even in battle.
In combat, Clay is rather laid back, in contrast to the slightly more serious Akane. He is almost always smiling, and seems to be quite confident in his and Akane's skills as a Weapon and Meister, not panicking when fighting, even if the opponent is a Traitor.
Despite his laidback nature, he is still formal to his peers and his seniors, not hesitating to be of help. He cares for the people around him though, as he only gets worried when other people might be in trouble, and often does not hesitate to intervene. Clay tries to introduce himself as calm and informal in front of the NOT trio, looking relaxed as he simply introduces himself with "Yo." But he can be more emphatic than Akane, not only due to his nervousness but, especially after Shaula kills Sid, concern for Anya's safety and those at the DWMA battling Shaula.
Although he is observant, Clay's analytical skills are limited by certain circumstances. He seems to lack the same level of observance as Akane, tending to be gullible or taking circumstances at face value. For example, he believes Akane's offer for the two of them to dress as witches for Trick or Treating and hunting witches on Halloween. As well, when Akane compliments the taste of the Master's coffee, Clay admits that he cannot tell whether the taste is good or not, and that he thought that the Master's shop would not be so well-run due to it accepting part-time DWMA students. Even when Shaula was right in front of him, disguised as one of many vendors before the Halloween Death Festival, Clay did not spot her, although this may be because he never saw her face-to-face before, instead relying on a police sketch of her and the fact that she was dressed as in a common witch Halloween costume, like many other vendors.
Clay's enthusiasm and nervousness can be raised quite easily, making it more difficult for him to think of alibis, stay undercover, and focus on tasks. When he felt enthusiastic about working at Deathbucks, after getting changed into his waiter's uniform, Akane jokingly called him "simple-minded." Such high energy causes him to misspeak at times, as Akane calls him "smart, but [...] not very quick on your feet." He is surprised how well Akane can improvise successful abilis that do not seem convincing to him, and how Akane can observe objects nearby that he can use as cover stories, such as a box of donuts to excuse his visit to Sid's Anti-Witch Headquarters. In contrast, Clay tends to sweat and struggle to speak.
Clay's tendency to speak before he thinks can lead him to over-complicate a simple topic, such as his complex flow-chart of their friends' relationships to cover for his and Akane's undercover security detail on Anya, or can demonstrate his failure to anticipate ramifications of his words, such as his inadvertent insult towards the indecisive Tsugumi when noticing that it is rare for a weapon to have two meisters. Clay can feel so overwhelmed by such difficulties that he forgets how he caused such problems, feeling humiliated and apologetic.
Clay is relatively tall and slender in stature, while noticeably older than Tsugumi Harudori and the majority of his fellow classmates. His age has been estimated to be around that of a high school student, making him anywhere in between sixteen and eighteen years old. He also features spiky and light-colored hair.
While taking courses as a NOT student, his typical attire consists of a simple pair of black trousers accompanied by a white shirt, usually left unbuttoned at the collar, and solid black tie, which is further adorned by the presence of a small Shinigami mask icon near its tip. This clothing is completed by a simple pair of black leather shoes and a light-colored belt, which occasionally has a small pouch attached to it on Clay's right side. The combination of this formal attire and Clay's natural physical proportions can falsely give the impression that he is a senior at the DWMA, rather than his actual position as a freshman. While Akane tends to wear a full suit with his tie properly pulled to his collar, Clay tends to wear his collar unbuttoned and his tie loosened.
During the brief period that he serves as a waiter at a Death City café, Clay adopts the typical uniform of the establishment, which is comprised of a white shirt with rolled-up sleeves that is accentuated by a black bow tie, as well as a dark waistcoat with pockets holding a few pens and trousers. Due to the nature of the profession, he also wears a black apron that is tied at the waist and features a small Shinigami emblem.
- Demon Great Sword (魔大剣, Madaiken): In his fully transformed state, Clay assumes the form of an elegantly crafted and slender great sword that features a solid black blade, surrounded in its entirety by a narrow white cutting-edge. However, the most unusual portion of this weapon is its hilt, which consists of a completely smooth cylindrical handle, attached by an unconventional arrangement of two small diamonds that form its guard. The tip of this sword is incredibly sharp, requiring only the slightest of pressure to pierce human flesh.
Analytical Skills: Clay possess amazing analytical skills and earned praise even a fellow CIA member and three-star Meister Sid Barrett, who also told him his skills in analysis was something required and valued within the DWMA-CIA. Clay's research skills allowed him to narrow down the identity of the Traitors' leader to Shaula Gorgon, instrumental to locating and defeating her. Clay is also skilled at tracking patterns of attacks on Death City and anticipating ominous signs, such as when he noticed that Traitor attacks had slowed down, potentially foreshadowing that Shaula was planning a new attack.
Acting upon his mission in infiltrating the NOT class to secretly protect Anastasia, Clay attends the entrance ceremony at Death Weapon Meister Academy, seating himself alongside the other NOT class students beside his meister. Shortly after Sid's dismissal, Akane and Clay chances upon a skirmish occurring between Anya and Tsugumi against Hao and Raid. Akane stops Clay, wanting to see how the two would fare. However, he is reluctant and surprised to see Sid, who had appear behind them, will not intervene in the skirmish.
He then proceeds to watch the fight in its entirety due to Sid's reluctance to interfere. During the fight, Akane humorously pushes his face upon Tsugumi's weapon form revealed to be a halberd. however, after the fights conclusion, Clay volunteers to alert Medusa Gorgon about the status of the injured party.
In an anime-only scene, 
Choosing to seek employment at Master's Café (also known as Deathbucks Café), Akane and Clay are greeted with the familiar faces of Tsugumi Harudori, Meme Tatane and Anya Hepburn, where the pair then exchange introductions with their fellow students. Questioned about their reasons for attending a part-time job, Akane asserts that Clay had spent their entire allowance on playing games at an arcade, something which Clay attempts to refute but is prevented from doing so due to a quick glance from his Meister. After changing into their respective waiter uniforms, the motivated pair begin to attend to their duties, while remaining worried about both Tsugumi's and Meme's attempts at work, although he is rather impressed by Anya's incredible enthusiasm. During a short coffee break; Akane remarks about the deliciousness of the Master's coffee, resulting in Clay's admittance that he couldn't tell and instead believed that the café would be rather shoddy due simply to its hiring of part-timers, however, this thought is interrupted by the arrival of Ox Ford, with Akane cutting off his partner to explicitly refer to him as "senpai".
Seeing out the rest of the week, both Akane and Clay receive their pay and thanks from the café's Master at the jobs conclusion.
Overhearing Sid's conversation about another traitor-related incident, both Clay and Akane request to deal with the traitor by scaring the other off with their skill. Later, the duo confront the strange traitor. Suggesting to his meister to point his sword at him and the other following his suggestion, Akane tells the man to give up. To his surprise, he leans over and attempts to retaliate, only to be beaten by a single blow from Akane.
Arriving late to their scheduled class, Clay apologizes for their delay after Maka Albarn and Soul Eater Evans's performance concludes, just before Akane blames their tardiness being caused by Clay goofing around at the game centre once again, much to the latter's annoyance. He watches his meister recount to Sid the details of the both of them deciding to detain the strange traitor due to his abnormal behavior.
Appearing just in time to prevent Shaula's servant from inflicting further harm on Anya, Meme, and Tsugumi, Akane and Clay intervene as the former uses Soul Menace to separate both parties. Akane informs the traitor that they're not fighting agents of the DWMA and asks the assailant to leave, declaring her won't find much of a challenge with them. Seeing the traitor leave, both Akane and Clay takes them back to their dorm.
On the day of the Athletics Test for the NOT class, Clay Sizemore completes the meter dash run with a score of 10.18, earning the admiration of the NOT class's girls and placing him as the top weapon in the class, though advises his meister to not overdo it due to his usually high score. He later watches his meister give Tsugumi some encouragement on her performance in the Athletics Test for the first time.
Sid calls for both Akane and Clay as they head to the Death City's holding area for inmates as they investigate the Traitor incident. Arriving at the holding area, it is breached by Shaula's servant, who has managed to kill the suspect in custody that was knocked out by Akane and Clay days earlier. Sid tasks Clay and Akane with chasing the murderer while Sid checks out the crime scene.
After a disembodied Tezca Tlipoca identifies the moon as a potential place of residence for the Kishin, Asura, and with the confirmation of this suspicion due to Maka Albarn's Soul Perception ability, Shinigami orders that preparations be undertaken in anticipation for the final confrontation. With Franken Stein assuming command over the entire operation, Sid instead goes and instructs both Akane and Clay to provide assistance.
He and Akane encounter into Noah and Gopher, neither knew who they were. After ignoring them, Akane decides to go in the cave with Noah and Gopher behind them which Clay said is a bad idea. He and Clay met up with Sid with Noah and Gopher behind them, which shocked Sid. Clay made up some excuse which only angered Sid. Akane explained he brought them to "use" them (Noah and Gopher says the opposite). While walking to the end of the cave, they found a huge pitch black pit. Sid dropped a flare only to wake up Asura. However, it was only a hallucination; hence proving Asura is there.
- Both Clay's name and his respective weapon form are an allusion to a claymore (クレイモア, kureimoa), a traditional two-handed longsword used by the Scottish Highlanders in Scotland.
- ↑ 1.0 1.1 1.2 Soul Eater Manga: Volume 21, Chapter 90, Yen Press English edition, Page 100
- ↑ Godswill Ugwa, "Soul Eater Not! English Cast Announcement." Funimation. 23 Apr. 2015. Accessed 23 Apr. 2015. http://www.funimation.com/blog/2015/04/23/soul-eater-not-english-cast-announcement
- ↑ (Yen Press)Soul Eater Not! —Tsugumi:They look about high school age. — In Japan (because Tsugumi is from there as well as the author making the point), the average age for those in High School is 15-18 according to this.
- ↑ Soul Eater Not! Manga: Chapter 39
- ↑ Soul Eater Not! Manga: Volume 1, Chapter 4, Yen Press English eBook, Pages 167, 168.
- ↑ Soul Eater Not! Manga: Volume 1, Chapter 3, Yen Press English eBook, Page 98
- ↑ 7.0 7.1 Soul Eater Not! Manga: Chapter 35
- ↑ Soul Eater Not! Manga: Chapter 36
- ↑ Soul Eater Not! Manga: Chapter 3
- ↑ Soul Eater Not! Manga: Volume 2, Chapter 14, Yen Press English eBook, Page 177
- ↑ 11.0 11.1 11.2 11.3 Soul Eater Not! Manga: Chapter 21
- ↑ 12.0 12.1 12.2 Soul Eater Not! Manga: Chapter 13
- ↑ 13.0 13.1 Soul Eater Not! Manga: Chapter 34
- ↑ Soul Eater Not! Chapter 3, page 15
- ↑ Soul Eater Not! Manga: Volume 4, Chapter 22, Yen Press English eBook, Page 40
- ↑ Soul Eater Not! Chapter 3, page 17
- ↑ Soul Eater Manga: Chapter 4
- ↑ Soul Eater Not! Chapter 4, page 4
- ↑ Soul Eater x Soul Eater Not! mobile game.
- ↑ Soul Eater Not! Anime: Episode 12
- ↑ Soul Eater Not! Volume 2; Chapter 14, page 178
- ↑ Soul Eater Not! Manga: Chapter 14
- ↑ Cite error: Invalid
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- ↑ Soul Eater Not! Volume 1; Chapter 1, page 26
- ↑ Soul Eater Not! Volume 1; Chapter 1, page 40 (eBook)
- ↑ Soul Eater Not! Chapter 1, pages 45-48 (eBook)
- ↑ Soul Eater Not! Anime: Episode 2
- ↑ Soul Eater Not! Volume 1, Chapter 3, pages 100-113 (eBook)
- ↑ Soul Eater Not! Chapter 3, page 32
- ↑ Soul Eater Not! Volume 4; Chapter 4, page 125-129
- ↑ Soul Eater Not! Volume 1; Chapter 4, page 144-145 (ebook)
- ↑ Soul Eater Not! Volume 1; Chapter 4, page 168-171 (ebook)
- ↑ Soul Eater Not! Manga: Chapter 7
- ↑ Soul Eater Not! Manga: Chapter 8