TV-Series
Description
Itsuki Sumeragi is a first-year student at Hyakkaou Private Academy, where she belongs to the prestigious flower class and initially holds a position on the student council. Her prominent family background, as the daughter of the president of a leading toy company in Japan, provides her with immense wealth and influence that she uses to navigate the school's gambling-centric hierarchy.

In appearance, Itsuki has chin-length light caramel brown hair with bangs swept to the right, a green hairband, and blue eyes. She wears the standard Hyakkaou Academy uniform of a red blazer with black trim and gold buttons over a white button-up shirt with a black tie, paired with a pleated skirt and black stockings that feature silver star designs on the sides. Her nails are notably painted pink with decorations, which appear as stars in the anime version and club suit symbols in the manga.

When first introduced, Itsuki presents a friendly exterior but quickly reveals a manipulative and sadistic personality. She has a disturbing hobby of collecting the painted fingernails of those she defeats in gambling matches, keeping them as trophies of her victories. Her approach to gambling is business-like and calculating; she uses her family's resources to create rigged games and cheating tools, such as temperature-sensitive marked cards, to ensure she never loses. Despite this confidence, Itsuki is ultimately cowardly at her core. When faced with genuine risk or the possibility of losing something precious, her composed facade crumbles, revealing insecurity and a desperate fear of loss.

Itsuki's primary motivation is power and status. She purchased her seat on the student council using her family fortune and is driven by a desire to climb the social hierarchy of Hyakkaou Academy. Her father is described as a practical and strict man, and she fears being disinherited if she fails to secure powerful connections at the school. This fear fuels her ambition to regain her council position after losing it and even dream of becoming student council president herself one day.

In the story, Itsuki serves as an early antagonist who challenges the protagonist Yumeko Jabami to a card game called Double Concentration. Confident in her cheating method, she bets Yumeko's fingernails but is exposed and decisively defeated. Following this loss, she is expelled from the student council but remains a recurring presence. She later approaches Yumeko as an ally, hoping that Yumeko will eventually defeat the student council president and allow Itsuki to reclaim her former position. During a high-stakes gambling match against the student council treasurer Kaede Manyuda, Itsuki becomes a crucial partner, using her wealth to fund the bet and even ripping off her own nails to stake her life's worth in a dramatic display of commitment.

Itsuki develops several key relationships over the course of the series. Her connection to Yumeko Jabami evolves from one of arrogant challenger to humbled defeat and then to a strategic alliance built on mutual benefit. More significantly, she harbors deep romantic feelings for Kaede Manyuda, which become a central part of her character development. After Kaede loses everything in a gamble, she holds his life plan and devotes herself to his care and recovery, even sacrificing her own success in the student council election to help restore his spirit. She also shows a growing capacity for genuine friendship, particularly with Mary Saotome in spin-off material.

Throughout the series, Itsuki undergoes notable development. She begins as a character who relies entirely on cheating and her family's wealth, believing these to be the only paths to success. Her defeat by Yumeko forces her to confront her own cowardice and reliance on unfair advantages. Through her subsequent gambles and her relationship with Kaede, she learns to take genuine risks, showing bravery she never knew she had. By the end of the election arc, she has abandoned her nail-collecting hobby and no longer decorates her nails, symbolizing her rejection of her past obsession with trophies and status symbols. Her motivations shift from purely selfish ambition to include emotional investment in others, particularly her willingness to lose everything for Kaede's sake.

Itsuki possesses several notable abilities, primarily centered on gambling. She has an exceptional memory, which is a significant asset in card-based games. Her family's toy company allows her to access custom-made gambling tools, and she has demonstrated the ability to cheat with marked and temperature-reactive cards. However, her most defining characteristic may be her access to vast financial resources, which she can deploy strategically to influence bets and outcomes. Over time, she also develops a genuine capacity for risk-taking and psychological manipulation, as seen when she and Yumeko collude to bluff Kaede into making a fatal mistake.