Kusuo Saiki (斉木 楠雄, さいき くすお lit. Saiki Kusuo) is the main protagonist of the series who has all kinds of ESP-related abilities. He usually avoids getting into troublesome situations. His trademark appearances contain his green-tinted glasses and two pink antennas located slightly above each ear which have the function of limiting his power. In the beginning, he was always seen alone but as the story progresses he eventually gets along with his schoolmates, especially Riki and Shun. Kusuo is one of the main characters of the series and was starred by Yamazaki Kento in the live action of the series.
As a child, Kusuo does not wear any limiter and has striking pink hair that differs from both of his parents. In his current image, he has a limiter on the both sides of his head which is never removed unless absolutely necessary or by accident. During his days at school, he wears the standard PK Academy uniform that all male students wear, while on his days off he wears clothes that are sewn by his mother. However there are times he is forced to buy clothes with Shun and Riki. Kusuo's appearance is not limited to that of a male, as he can also transform into anything (but it takes 2 hours to transform).
In his female form, Kusuo is first known as Kusuko (he later changes it to Kurikou),. The female form features lighter Pink hair and lacks limiters though she still wears glasses. In his cat form, Kusuo is known as Sai and has white fur. In this form he still wears his glasses and his limiter is in the form of a collar around his neck.
As of the finale, he no longer wears his limiters or glasses. However in the unadapted GIGA chapters, he reprised them as his powers begin to return.
As a Psi user, Kusuo is usually emotionless and constrains himself from having any friends, preferring to do whatever it takes to not to be associated with others so that he doesn't expose his powers. Due to this, he has never spoken using his voice, instead preferring to project his words via telepathy into the minds of others. Although he didn't have any friends first year, during his 2nd year, a lot of his classmates like Riki, Shun, Kineshi, Aren, Kokomi, Chiyo, Reita and Mikoto kept on bugging him and somehow changed his perspective. He later thought of himself as a friend of theirs and even outwardly called Shun his friend.
Although he doesn't express much interest in many things due to his powers (e.g. surprise parties, romance, fortune-telling, etc), Kusuo is addicted to the dessert known as coffee jello and can be persuaded to participate in anything his friends are in as long as he receives his coffee jello. His addiction is not just limited to coffee jello but also to different kinds of sweets. Despite being able to get anything he wants without using any money, Kusuo uses money and saves up money to buy something he wants, like the Coffee Jelly Maker. His kind mom was the sole reason why he didn't abuse his own psychic abilities for nefarious activities. Kusuo also has an interest in television shows, due to electronics (unless he uses his psychometry) being unaffected by his powers, allowing him to enjoy dramas/scenes that prevent the use of his telepathy which leaves him open to spoilers from the thoughts of others.
Kusuo was born in Hidariwakibara Town at the Middle-class area with his completely normal parents. During his mother's pregnancy, Kusuo was shown to have been chaging body and image wehn shown in CT scans. When he was bore in the hospital he came out as a girl but a minute later he became a boy. At the age of 1 years old, Kusuo was able to fly, teleport and use telepathy to communicate with his parents. Kusuo was then pursued by an Intelligence Agency of a certain nation for his powers when he was 4. Since then Kusuo conceal his powers to avoid unnecessary trouble and erased the Intelligence Agency along with the nation.
When he was 6 years old, he befriended Akechi Touma, an observant boy who mocks their classmates. Once when Kusuo was about to teleport behind the bush due to a certain television show he wanted to watch, he witnessed his classmates bullying Touma who lost his consciousness afterwards. Thinking Touma has passed out, Kusuo healed him by touching the tip of his shoe to Touma's arm and left not knowing he dropped his name tag. The next day, on PE class, Touma was mocking again the bully in front of his classmates when he was about to be hit again but Kusuo used his powers to their classmate. At that moment Touma loudly exclaimed that Kusuo is an Esper but Kusuo didn't say a word about it.
Kusuo was hesitant to say anything but he was friendly with Touma and since then the two were seen together. Kusuo always see using his clairvoyance how their classmates bully Touma like taking his shoes. Then one day, Kusuo went home without Touma when he suddenly turn back to the school and found Touma has been knocked out by his classmates and is been made fun of. Kusuo went mad and destroyed the whole school. The next scene shows the destruction of the grade school Kusuo attended and the bodies of injured children on the ground with Kusuo standing with a stolid face.
When he turned 15 years old, his abilities increased and was able to use telekinesis, X-Ray vision, and many more ESP related powers, which he thinks are nothing but trouble. His power to control his appearance has not yet been developed as people can see the antennae on his head. Kusuo had been keeping his distance from his classmates but Riki, known as their delinquent was bullying him. Riki only became friendly with Kusuo when he implicitly helped Riki from being framed by Takahashi as the thief. After the two got friendly, Shun went to befriend Kusuo who then rejected the later's quest on finding the mysterious alien (which is actually just Kusuo). After learning the reason why Shun insist on becoming his friend, Kusuo finally gave up and transformed into the alien that Shun was looking for. The three started to hangout since then.
During his 2nd year, a lot of his classmates like Riki, Shun, Kineshi, Aren, Kokomi, Chiyo, Reita and Mikoto kept on bugging him and somehow changed his perspective. He later thought of himself as a friend of theirs and even called Shun his friend.
When Touma came back to Hidariwakibara Town, he was nosy about Kusuo's circumstances as he suspects Kusuo as an esper. When Touma confronted Kusuo about the incident at their old grade school, Kusuo was hesitant so he petrified Touma first then he tried to change the course of the story by going back to the past the day before Kusuo rampaged on the grade school. He then went back to the current time he was originally in and remove the petrification on Touma. He then decided to tell Touma about his powers. Thus, Touma is the 3rd person in the PK Academy to know that he is a psycic.
These are the alternate worlds that was introduced in the series.
Censored World -Kusuo didn't enroll in PK Academy and then was thus unable to mingle and talk to the other students/characters. He then turned the world into a censored world in just 10 chapters. Instead, the other work of the author, the Mikami Case Files was serialized.
Modified 2014 World -Kusuo influenced the meeting of his parents encounter which changed the flow of the events. Kusuke created a time machine which was the cause for the World War 3 to break out and the world met it's destruction. The cause of Kusuo's death was unclear but in Modified 2014 World, he has been dead for more than 3 years.
Unable To Save The Dog World -In Chapter 1 or Episode 1, in another world "Kusuo" wasn't able to save the dog from the incoming truck. Devastated by the accident and his hesitant attitude, "Kusuo" decided to change for the better and used his psychic powers as people came to ask for his help.
(To himself) "I am the world's unhappiest man who has had everything snatched away since the moment of my birth."
(To Nendou) "What a truly terrifying man you are, Nendou Riki. I'd prefer to kill you before you can kill me."
(To Kaidou) "Honestly, what a moron. Sorry for saying you have chuunibyou. You don't possess any sort of power but your actions were by far no means possible for the average person."
(To himself) "I messed up, an image of father came up for a second. It seems like he's doing his work happily today too. This screw up really hurts me in many ways."
(To Chiyo) "Don't think it will be easy to get a flag with me as your opponent."
(To Kineshi) "I don't care about your likability rating of me."
(To Kineshi) "I hate attracting attention but I hate owing someone even more."
(To Kurumi & Kuniharu) "My powers are not perfect after all."
(To Shun) "He should really choose his friends more wisely. This is just some advice from a friend."
(To Kokomi) "Your summer is sad too."
(To himself) "First, the bug I can't read and now comes the Nendou I can't read. Give me a break, I am NG with N or G."
(To Reita) "You were born into a temple family but you're full of desires. I've never seen anyone so dirty with such clear eyes."
(To Reita) "If you talk, you die."
(To Reita) "Go complain to the author."
(To Reita) "Well, don't let it get you down. There are as many girls as there are stars in the sky. Although stars are always out of reach."
(To Chiyo) "There's no other way. I guess I will become the shelter who will protect the couple's umbrella."
(To himself) "I guess if you do something good, good things will happen to you."
(To Kuniharu) "I would rather watch butt exercises than listen to fortune telling."
(About Kokomi) "I never expect her to go that far, all for the sake of being perfect. Perhaps she is close to perfect, huh."
(About Christmas) "Whereever there is light, there is also darkness... Even a seemingly blissful atmosphere like this gets over-shadowed by the darkness inside people's hearts."
(About Matsuzaki) "But I don't hate teachers like him. He's a strong ally for weak willed students like myself."
(About fighting Nendou's ghost) "Now then, here's a question for you. This means I've changed from psychic to ghost so in pokemon, how effective is ghost against ghost? The answer is super effective."
(Without his telepathic powers) "H-how is everyone so composed? Haven't they considered that there might be a killer next to them without them knowing it?"
(About Makoto) " I had no idea... Who knew he was that kind of guy who had far surpassing the limits of a sister complex."
(When Shun and Riki competes in game) " Now that I think about it, I didn't use any ESP this time. Well whatever. It would be rude to interfere in a showdown between men."
(Abut Chisato's work) "What a pain... I can't make fun of Kaidou anymore after all these talk about seals and changing the world. But I had to pay her back for the Coffee Jelly."
(To Reita) "Peeping is a crime you know. You're coming with me to the police. You think someone who was 'only looking a little' would be depicted as a silhouette like some criminal in Conan? Not to mention all that panting. That's definitely something a sexual predator would do."
(About Kokomi) "What a pain. It's frightening that she was actually going to get it. But it's no use. Puppy dog eyes won't work on an esper like me."
(When asked by Shun about his glasses fogging) "You'd understand my point if you had permanent x-ray vision, too."
(After losing his wallet) "They pick-pocketed me? Me? Me of all people? The same as Takahashi? On the same level as that? I have never felt so humiliated."
(To the thief) "You laid your hands on an psychic's wallet. I hope you're prepared for the consequences."
(About the new transfer student) "Just great... you shouldn't be expecting anything from a new student, or have you forgotten that last atrocity? The author's just introducing a new character to get himself out of the rut. It's a cheap tactic."
(About Midori's face) "I understand your feelings Kaidou but you're staring way too much."
(About Cafe Mami) "Even when you were so depressed and emotionally unstable, the taste of your coffee jelly stayed the same. This is undeniably the work of a pro and that's why the customers will return on their own even without using ESP."
His name, Saiki Kusuo, is a pun on the word Psychic (サイキック lit. Saikikku).
His gender bender name are Kusuko and Kuriko.
He is scared of bugs and Riki because he can't read their minds; insects being too small and Riki too stupid. He appears to have inherited his fear of bugs from his father.
His Zodiac sign is Leo.
He made a small cameo in Assassination Classroom, while his limiter made a cameo in Gintama.
He hates being in someone's debt.
He never talks using his voice.
He does once in the final chapter.
He has been 2nd year 4 times due to resetting the Earth many times.
He is the reason why they stayed young because he controlled the time.