A high school student known only as Kei navigates the treacherous world of Japan's underground mahjong parlors, where the stakes extend far beyond money to include personal assets, bodily organs, and human lives. Kei has earned the fearsome nickname K of the ICE for his cold, calculating playing style and his ability to maintain absolute composure under pressure. Despite his youth, his exceptional memory and analytical skills allow him to dominate in games where one wrong move can be fatal.

The story begins when Kei is dragged deeper into this criminal underworld by a man named Seki. After winning a particularly dangerous match, Kei has the opportunity to walk away with the prize money but instead makes a choice that changes everything. He uses his winnings to rescue Amina, a young foreign idol singer who is being held as a slave. Amina has been trafficked into Japan, has no legal status, and suffers from a severe renal disease that will require a transplant. Kei takes her into his home, and protecting her becomes his primary motivation, forcing him to remain in the mahjong underworld he might otherwise have escaped.

This decision sets Kei on a collision course with his greatest rival, Dojima, a flashy and intuitive player known as the Lion. Unlike Kei's cold, logical approach, Dojima plays by instinct and rides waves of luck, making him an unpredictable and formidable opponent. Their rivalry oscillates between fierce competition and grudging cooperation as circumstances repeatedly bring them together against common enemies.

The series follows the sequential arcs of the manga source material. In the initial storyline, Kei fights to secure his position and protect Amina while clashing with various underground figures. The Hitobashira-hen arc sees Kei teaming up with the Takatsu-gumi syndicate to face an even greater threat, resulting in a high-stakes battle where Kei suffers devastating physical consequences. After being forced to hang himself as payment for lost points, he survives but loses mobility, requiring a wheelchair and crutches to move. This arc culminates in Kei becoming enslaved to the very syndicate he once worked with, leading to his participation in a survival mahjong tournament as the only path to freedom.

Throughout these ordeals, Kei is supported and sometimes challenged by the people around him. Yuu Katsuragi, his childhood friend who harbors romantic feelings for him, struggles with his dangerous lifestyle. Her father was the one who taught Kei to play mahjong, creating a complicated bond between them. Other figures in the underground, including the cunning Takatsu and the dangerous Hatakeyama, constantly shift between ally and enemy as power dynamics change.

The live-action television adaptation brings this violent, desire-filled world to the screen with a cast including Maeda Goki as Kei, Ichinose Hidekazu as Dojima, and Akane as Amina. The series depicts the brutal reality of ura rate mahjong, where every hand dealt could mean financial ruin, physical mutilation, or death. As Kei fights to protect Amina and secure his own freedom, he must confront not only his opponents at the mahjong table but also the emotional scars of his past, including the childhood trauma of his younger brother being murdered by their own parents for insurance money. The tension between Kei's icy exterior and his desperate devotion to the people he cares about forms the emotional core of this crime thriller set against the backdrop of Japan's most dangerous gambling dens.