Kusuo Saiki has an average build and height, with fair skin, pale purple eyes that lack visible pupils, and distinctive short, hot pink hair. He is rarely seen without his psychic limiters, two devices attached to the sides of his head, resembling white and cyan antennae with pink, lollipop-like tips. These devices regulate his immense psychic powers and are only removed under extreme circumstances or by accident. Additionally, he wears white-framed glasses with lime green lenses designed to suppress his petrification ability.

During school, Kusuo wears the standard male uniform of PK Academy. On his days off, he sometimes wears clothes sewn by his mother, though he occasionally purchases his own due to her eccentric fashion sense.

Kusuo possesses the ability to transform into any living being, though each transformation lasts only two hours. In his female form, he goes by the name Kuriko (formerly Kusuko) and is depicted with longer, lighter pink hair, clear glasses, and no visible limiters, usually wearing the female PK Academy uniform. As a cat, he takes on the name Psi (or Sai) and has white fur. Even in this form, he retains his glasses and limiter, which appears as a collar.

As a child, Kusuo did not wear glasses or limiters, revealing his pale purple eyes. His signature pink hair, which differs from both of his parents, was present from birth until he later altered public perception using mind control to avoid standing out.

By the series finale, Kusuo no longer wears his glasses or limiters, having gained improved control over his powers. However, in the epilogue chapters, he resumes wearing them due to signs that his abilities are returning.

As the central character of The Disastrous Life of Saiki K., Kusuo Saiki’s narrative drives much of the series’ humor and introspection. His personality is complex and evolves over time, shaped heavily by the burden of his psychic abilities.

In his early childhood, Kusuo was expressive and emotionally open. Lacking full awareness of the consequences of his powers, he would often act mischievously, once teleporting away for hours just to see his parents panic, and unintentionally breaking a whack-a-mole machine with his strength while assuming the machine was praising him. However, as his powers continued to interfere with normal life and isolate him from others, Kusuo gradually closed himself off emotionally.

By the present day, Kusuo is quiet, reclusive, and deeply averse to attention. He rarely speaks aloud, instead communicating through telepathy, and often tries to avoid social interaction by acting indifferent or hiding altogether. Despite this, he possesses keen emotional intelligence and is adept at reading people’s desires, often using subtle manipulations to help others such as improving someone’s romantic favorability rating or defusing social tension without drawing attention to himself.

Though Kusuo prefers solitude, he is fundamentally kind-hearted and selfless. He frequently sacrifices his own comfort and desires for the benefit of others, such as giving away his beloved coffee jelly to help a child or ensuring others can enjoy themselves even if it means isolating himself. He dislikes burdening people or owing them favors and maintains a strong internal code of responsibility, as shown in his guilt for making his mother keep his powers a secret.

Kusuo is considered highly dependable. He helps with household chores, saves up money to buy things instead of using his powers for personal gain, and intentionally scores average on tests to avoid suspicion. He refrains from invading others’ privacy despite his telepathic abilities and tries to live as normally as possible.

However, Kusuo is not without flaws. While intellectually gifted, he sometimes lacks common sense, especially regarding modern technology and social norms such as nearly falling for an online shopping scam. He can also be prideful and stubborn, taking offense to minor insults (e.g., being pickpocketed despite being an esper) and refusing to admit things like seasickness. His pessimistic outlook and sarcastic internal commentary are recurring traits, but he is also open-minded enough to admit when he is wrong when presented with evidence.

Although Kusuo claims he does not believe he will fall in love, he shows curiosity about romantic relationships and often helps others with theirs. Aiura Mikoto, a fortune teller, predicts they are soulmates, adding another layer to his emotionally distant yet observant character.

Over time, Kusuo gradually begins to accept the friendships forced upon him by persistent classmates like Riki Nendou, Shun Kaidou, Kineshi Hairo, Kokomi Teruhashi, Chiyo Yumehara, Reita Toritsuka, Aren Kuboyasu, and Mikoto Aiura. While he initially had no interest in forming bonds, he eventually comes to care for his friends deeply so much so that he nearly reveals his psychic powers to them before ultimately choosing to keep it secret to avoid burdening them.

Due to his introverted personality and ability to read minds, Kusuo avoids social settings and instead enjoys solitary activities like reading, watching anime, and spending time in the school library. Since electronics are largely unaffected by his powers unless he actively uses psychometry, television and movies serve as rare forms of undisturbed entertainment though he avoids theaters to prevent receiving psychic “spoilers” from the audience.

Kusuo Saiki was born on August 16 to ordinary parents, housewife Kurumi Saiki and manga editor Kuniharu Saiki and was raised alongside his older brother, Kusuke Saiki. Even before birth, Kusuo displayed psychic abilities, including transformation, which could be seen in prenatal scans. At birth, he initially appeared as a girl but transformed into a boy within an hour. By two weeks old, he communicated via telepathy, and by one month, he was able to walk and fly. At just one year of age, he could run errands independently.

Kusuo’s psychic prowess drew early attention. In kindergarten, he consistently won games like rock-paper-scissors, even against teachers. After a frustrated teacher attempted to strike him, Kusuo’s existence began to draw attention online and on television. By the age of four, a foreign intelligence agency took interest in him, prompting Kusuo to erase the entire nation from existence to protect himself. From then on, he resolved to keep his powers hidden and began distancing himself from others.

At age six, Kusuo befriended Touma Asumi, a perceptive classmate. They first met during their elementary school entrance ceremony when Kusuo helped a nervous Touma who had an accident. Their friendship deepened until a pivotal moment when Kusuo accidentally healed Touma in front of him, revealing his abilities. Touma enthusiastically urged Kusuo to demonstrate more powers, and Kusuo agreed. However, after Touma told the class about his abilities, Kusuo panicked and destroyed their classroom, vowing never to reveal his powers again.

When an older Kusuo later traveled back in time, he altered these events. This time, he quietly helped Touma without being discovered, leaving behind only a name tag. Though Touma suspected the truth, Kusuo avoided confirming it and continued to protect him from the shadows. Eventually, when Touma was severely bullied and injured, Kusuo lost control, destroyed the classroom, and erased everyone’s memories including Touma’s.

Not long after, Kusuo began wearing his iconic green-tinted glasses, which he found in a toy box. These glasses suppressed his growing petrification ability. Around age 11, Kusuo also began wearing limiter devices on both sides of his head designed with help from Kusuke to suppress his overwhelming powers. While his left device effectively restricted his abilities, he later discovered that the right one had been booby-trapped by Kusuke to act as a “self-destruct” switch that would reveal his powers to the world. Their rivalry led to many attempts by Kusuke to remove it, all of which Kusuo thwarted.

Kusuo’s family moved frequently due to accidents caused by his psychic powers. Eventually, just before his first year of high school, they relocated to a house in Hidari Wakibara purchased from Kusuke and Kusuo enrolled in PK Academy at age 15.

Initially, Kusuo kept to himself and avoided interactions at PK Academy. The first person to speak to him was Riki Nendou, a loud and seemingly delinquent classmate who repeatedly asked to copy homework. Although Kusuo tried to avoid him, he discovered that he could not read Riki’s thoughts, a rarity and was surprised to find Riki genuinely kind and loyal. After Riki defended Kusuo from bullies, Kusuo began to accept his presence.

Shortly after, Shun Kaidou attempted to befriend Kusuo, under the pretense of searching for a mysterious alien (unaware it was Kusuo himself). After learning Shun’s true motive was simply to connect with him, Kusuo humored him by transforming into an alien and appearing before him, allowing their friendship to grow. The next day, the three began spending time together, marking the start of Kusuo’s expanding circle of companions.