Kurunu Sayu

Sayu Kurunu is a deuteragonist of Astral Academy. He is a 15-year-old, part-spider killer.

Personality
Sayu is an enthusiastic, high-energy young man. He is known for liking seemingly "unnatural" things, mostly things that are related to gore. He can stay in relatively high spirits even in sad or dire situations, and will often find a way to butt in the conversation or make rude remarks. He is very obnoxious and loud, polar opposites from Asahi, who he crushes on- who is shy, fidgety, and quiet. Sayu enjoys teasing people and making fun of them, especially of their struggles. Many students fear him and will walk away if they see him coming close. He sees himself as an evil person and will often cause unnecessary troubles to others.

He has an exaggerated sense of self-importance, bragging about his achievements and using them to belittle other people. Despite all of these traits, he has a good relationship with his parents, and is seen texting them on the phone.

In Chapter 9, after he saves Asahi from his kidnapping, he becomes more responsible and protective of his crush. This also causes him to become more violent, threatening to kill Kuroi on multiple occasions. When asked about it, Sayu says it wasn't because of love, but more because of the documents he came across while on the search for Asahi.

Early Life
Sayu was born with strange thin "spider legs" that he could control at will. His birth parents were scared of their child, and put him into an orphanage for adoption. He was eventually adopted by his current parents.

When he grew up, he discovered his wind powers, where he could cause small gusts to huge tornados with just a hand movement. Every night, he could catch a glimpse of a metallic creature- but he passed it off as a hallucination.

He was enrolled in the Luxis elementary and middle school by his parents. His obnoxious personality caused the other kids to ignore him and see him as an outcast, so he could never make friends. Because of this, he also thought that his unordinary wind powers were normal to kids his age. Sayu didn't like being treated as an outcast, so he started to bring a knife to school.

He saw Asahi for the first time in his first year of middle school, but due to the other wearing a hat to cover up his horns Sayu did not recognize him when he entered Astral Academy. He saw Asahi's paintings and thought they were beautiful. He was motivated to also start drawing because of it. Others at his school would describe them as gross or grotesque.

One day, Sayu was going to school to attend makeup classes. He wasn't particularly fond of makeup classes, so in the school lobby this anger manifested into a huge tornado. It left the school in shambles. Arizo arrived to the school while the tornado is wreaking havoc, and Sayu, noticing the door open, forces her onto the floor with his foot and kills her with the knife he brought. He then quickly leaves.

His parents, hearing the news, asked him if he was safe. He explained the situation, but removed all of the parts that incriminated him.

Soon after, at 7PM on a spring night, he found a letter while messing around with his wind powers. It was an invitation to Astral Academy- a whole new school.

Astral Academy First Year
Sayu is the secondary protagonist, who often hangs around with Asahi. He is very out of place and random, something that he says he's been ridiculed for. Since he's so close to Asahi, some students whisper that the half-spider is ruining the boy's reputation.

In Chapter 9, he teams up with Namida to save Asahi, who was kidnapped by Kuroi for the latter's research. They bump into some documents regarding Kuroi and his relationship with the Principal. He then goes into Kuroi's research lab and break the chains Asahi was trapped under with his knife. He and Namida then grab Asahi's unconscious body and leave. Kuroi tries to chase after them but can't detect their location.

After that, Sayu helps Asahi move around since the other can't move without limping, or completely collapsing. Asahi says it's like he was affected by a sleeping drug (which was the truth). The day goes by as usual, until a loud shake was heard.

In Chapter 11, when Kuroi is having a breakdown, Sayu uses his vulnerable state to stab him, which ultimately kills him. Sayu's spider legs have long reach, and Kuroi could be seen coughing up blood.

Miyasaza Kuroi
Although the two are similar, Sayu hates Kuroi with a passion. The main reason for this is because of his kidnapping of Asahi. Sayu stabs in Chapter 11 and kills him.

Niyada Asahi
He likes Asahi, and makes it quite clear in Chapter 4, but the other is too dumb to realize that. Since he likes people that can be easily manipulated, Asahi is his type. He will either play pranks on him or whisper people's deepest, darkest secrets to them.

Takumei Zenya
Zenya sees Sayu as a weirdo, especially due to his liking of gore and creepy things. Sayu gets pouty when Zenya says something against him. The two are still on good terms and Zenya is shown to be more polite to Sayu during school hours.

Kagami Namida
Friends who are on good terms. Kagami isn't a fan of his messy hair.

In Chapter 9, while they're on their way to rescue Asahi, they team up and investigate the school. They also find documented files about Kuroi and the Principal's words regarding him.

Trivia

 * Sayu is scared of making his closest friends hate him, so he isn't hesitant to lie to protect himself.