Gugu-Gaga is a 7-year-old girl and an apprentice ninja in the first grade of the ninja school. She always wears her favorite black penguin hood and dreams of becoming the strongest Dark Ninja in the future. She works hard at training with kunai and shuriken, but she is still inexperienced and often panics when her ninjutsu fails. She has a clumsy side, such as tripping or making noise during stealth missions. While she is good at moving quickly and is full of curiosity, she is also a bit of a scaredy-cat and sometimes hides her face in her penguin hood when faced with a strong-looking opponent. However, she has a kind heart and will muster her courage to help her friends when they are in danger. She is a hard worker who doesn't give up even after failing. Her usual catchphrase is "Nin-nin!" and she characteristically ends her sentences with "Guga."

Riri-Gaga is a 7-year-old girl in the first grade of the ninja school. She is a petite ninja who wears a black hood with a penguin motif and hides her mouth with a black cloth. She usually speaks at her own pace, adding "Guga" to the end of her sentences, but she is actually so capable that she stands apart from her classmates. She excels in situational judgment, physical ability, and the art of erasing her presence, making her a genius ninja with a practical sense despite her young age. She is particularly skilled in infiltration and surprise attacks, demonstrating abilities that rival adults when navigating darkness or complex terrain. On the other hand, she is as curious as any child her age and sometimes her eyes sparkle when she finds something interesting, even during a mission. Because her innocent and adorable behavior is usually prominent, those around her often think of her as a little mascot, but her expression changes completely once a mission begins, and she acts calmly and swiftly. She doesn't think of her own abilities as special and continues her training with the feeling that being able to do these things is only natural. However, due to her overwhelming talent and effort, her teachers have high expectations for her future. Her penguin hood is her favorite item and serves as her mark as a ninja, while also being a trademark that symbolizes the gap between her cuteness and her unfathomable skill.

Reiga is a 7-year-old girl in the first grade of the ninja school. She is a petite and adorable ninja wearing her trademark penguin hood, but she is actually a genius ninja who stands apart from her classmates. Despite her youth, she possesses extraordinary observation and judgment skills, allowing her to predict an opponent's next move from the slightest motion. She demonstrates skills that rival upperclassmen in many fields such as shurikenjutsu, martial arts, and stealth. Her ability to erase her presence is so perfected that even teachers sometimes fail to notice her approach. While she easily completes tasks that other students struggle with in class, she never flaunts her abilities. She usually behaves innocently, peeking out from under her penguin hood with large eyes, so only a few people in the school know her true strength. She has little awareness of being exceptionally gifted and often thinks her feats are only natural, but the moment a comrade is in danger, her childish atmosphere vanishes. She can suppress enemies with calm and precise judgment, showing strength that one would not expect from a 7-year-old.

Master Hyoga is a mysterious and highly skilled ninja who instructs the first-year students at the ninja school. A petite figure characterized by a hood with a penguin face drawn on it and pitch-black ninja attire. Although appearing cute, their skill reigns at the top of the ninja world, boasting extraordinary proficiency in martial arts, ninjutsu, swordsmanship, and stealth, overwhelming any powerful enemy with a cool face. Called "Master Hyoga" because of their movements as silent as ice, even seasoned ninjas lose track of them when they erase their presence. Usually gentle and caring, they are tolerant of students' failures and value finding and developing each individual's strengths. They also have a playful side, making jokes or doting on penguin-themed items, and are beloved by students as a reliable mentor. However, they show a rare sternness toward life-threateningly dangerous actions or behavior that abandons comrades, teaching what is truly important as a ninja. They hide an overwhelming strength unimaginable from their usual soft atmosphere, and few have ever seen them truly serious.

Guren is a former student of the ninja school and is currently a most-wanted criminal who has rebelled against ninja society itself. She completely rejects the teachings and rules of the ninja school and treats even former classmates and teachers as enemies without mercy. Not only did she betray the school, but she also aims to crush the school's ruling system and reshape the ninja world with her own power. She is feared by the school as an extremely dangerous traitor, and although capture and execution orders have been issued, the ninjas sent after her are being defeated one after another. Contrary to her petite and cute appearance, her combat ability is beyond common sense, and she is powerful enough to overwhelm multiple high-ranking ninjas simultaneously. Her greatest trump card is the ultimate ninjutsu "Gurenge," which she developed independently by ignoring existing ninjutsu systems. It boasts overwhelming firepower and destructive force, and few know its full extent. Her personality is cold and fearless; she never changes her mind even when persuaded by former allies and will crush anyone who stands in her way. To Guren, the ninja school is no longer a place to return to, but a nemesis that she must one day strike down with her own hands.

Gunjo is a former student of the ninja school and currently works as a ninja under the rebel Guren. Although in the position of Guren's subordinate, her strength cannot be underestimated, and she possesses combat abilities that ordinary ninjas cannot match. She masters the self-taught "Toren Ninjutsu," specializing in elusive techniques reminiscent of wisteria flowers and tricky battle styles combining shuriken and kunai. While she still has some inexperienced aspects and her judgment of battle situations and precision of ninjutsu remain immature, she confuses enemies with her inherent speed and insight. A young powerhouse who continues to fight in search of further strength, carrying loyalty to Guren in her heart.