There is a tower that summons chosen people called "Regulars" with the promise of granting their deepest desires. Whether it be wealth, fame, authority, or something that surpasses them all—everything awaits those who reach the top. Twenty-Fifth Bam is a boy who had only known a dark cave, a dirty cloth, and an unreachable light his entire life. So when a girl named Rachel came to him through the light, his entire world changed. Becoming close friends with Rachel, he learned various things about the outside world from her. But when Rachel says she must leave him to climb the Tower, his world shatters around him. Vowing to follow after her no matter what it takes, he sets his sight on the tower, and a miracle occurs. Thus begins the journey of Bam, a young boy who was not chosen by the Tower but opened its gates by himself. They call his kind "Irregulars"—beings that have shaken the very foundation of the Tower each time they set foot inside it.

On the 20th floor of the Tower, the "Regulars" who have been permitted to enter have to undertake arduous and extremely expensive tests to rank up. Most abandon hope and choose to stay where they are—but not Ja Wangnan. Wangnan is determined to reach the top and become the king of the Tower. However, he is weak and has repeatedly failed the exam, with debt collectors tailing him. In desperation, he attempts the exam one more time, only to encounter a mysterious and powerful individual: Jyu Viole Grace, a member of the crime syndicate FUG. Cursing his rotten luck, Wangnan has no choice but to form alliances with strong people, including Viole—who still refuses to be part of any team. Amid a dire situation, Wangnan must find a way to change Viole's mind to finally advance past the 20th floor, or he will never get a chance to build his legacy.