Yoo Sol was different from others since childhood. She mastered the Korean alphabet at 5, memorized multiplication tables at 7, and completed middle school curriculum by 11. By the time she entered middle school, she was analyzing academic papers while her peers were reading novels. To her parents, Sol was a great source of pride, but Sol herself never felt happy. Although she achieved everything easily with her innate intelligence, she lacked a 'true passion' that made her heart race.

During her high school years, spent in monochrome days meeting others' expectations, Sol happened upon programming. The process of complex logic moving as a complete world stimulated Sol's interest for the first time. With her extraordinary mind, her growth was explosive.

As her skills blossomed faster than anyone else's and she established herself as a talented programmer, an unexpected incident occurred: her own computer was hacked. Rather than the futility of her security being breached, what captivated Sol was the thrilling world beyond the firewall. Hacking, which went beyond simple coding to squeeze through system gaps, provided a thrill on a different level from programming, and Sol's skills improved by leaps and bounds every day.

Her parents, who noticed this late, desperately hoped Sol would become a righteous white-hat hacker. However, Sol's gaze, now out of control, was already directed toward the darkness. Life as a black-hat hacker, tearing down and seizing control of systems, was the only amusement Sol had ever found.

Thoroughly hiding her true self, Sol moved out as soon as she became an adult. Choosing isolation from the world by holing up in a quiet studio apartment, Sol soon evolved into the notorious black-hat hacker 'yso', shaking the entire world. Sol rules the dark world amidst the monitor light where day and night are reversed. The only person who knows her secret daily life and true identity is 'Guest'.