Joong-Hyuk Yoo is a central figure in the narrative, originally known as the protagonist of a web novel that suddenly becomes reality. His background is shrouded in mystery, as he has no memories of his youth or family, essentially coming into existence as an adult with skills as a professional gamer before the scenarios began. This career as a pro gamer grants him a natural, almost god-like adaptability and advantage in any game-like situation. His most defining characteristic is his status as a regressor, a person who sends his consciousness back in time to the beginning of the apocalyptic scenarios upon death, retaining all memories from his previous failed attempts. The story primarily follows him during what is known as his third regression, though it is later revealed to be his 1864th, following immense memory loss from a traumatic prior round.

Personality-wise, Joong-Hyuk is described as someone designed to be tougher in body and nobler in heart than any other creature, yet the immense trauma of living through hundreds of regressions has profoundly changed him. He is normally very confident in his abilities, never backing down from a challenge and displaying extreme talent in numerous fields, from swordsmanship to cooking, the latter of which he is so skilled at that he refuses to eat anyone else's food. His speech is characteristically concise, blunt, and often rude, expressing himself more through actions or subtle physical cues, such as dragging his sword tip along the ground when pleased or his left eyebrow twitching when making a serious decision.

The repeated cycles of failure and loss have made him calculating and cold, willing to kill those he deems threats and distance himself from companions as a defense mechanism against the pain of losing them. This has led to a psychological condition known as regression depression, where even small failures make him lose hope and consider giving up to reset the round. In his most advanced regressions, this depression can cause him to fall into a completely unresponsive, dissociative state.

Joong-Hyuk's primary motivation is to reach the end of the scenarios, a singular goal he pursues with resolute determination no matter the cost. Though it seems contradictory to his cold exterior, he does naturally fight for the greater good, a remnant of his original caring nature. Within the story, his role is that of the powerful, pre-established protagonist whose path is disrupted by the arrival of Kim Dok-Ja, the sole reader of the original novel. Initially suspicious, Joong-Hyuk comes to rely on Dok-Ja's unique knowledge of the future, and their relationship evolves into that of "Life and Death Companions," a bond so strong it is recognized by the Star Stream itself. Despite their outwardly rude and insulting dynamic, with Dok-Ja often calling him an "emo bastard" or "sunfish bastard," there is deep trust and protection between them. To Kim Dok-Ja, Joong-Hyuk acted as a father, brother, and best friend during his difficult childhood, and in turn, Joong-Hyuk becomes fiercely protective of Dok-Ja, often being the first to notice when Dok-Ja is planning a self-sacrificial move.

Beyond his bond with Dok-Ja, Joong-Hyuk has key relationships with other survivors, though he maintains a certain distance. He eventually recruits figures like the resilient warrior Lee Ji-Hye and others into his party, looking out for them in his own harsh way despite his rudeness. His development throughout the narrative shows a gradual warming from his harsher instincts, as his interactions with Dok-Ja and the new variables in his regression help him begin to overcome his survival-driven isolation.

Joong-Hyuk possesses a vast array of notable abilities befitting his status as a protagonist. His most powerful ability is the stigma Regression, which allows him to send his consciousness back to the start of the scenarios with all memories intact, though he must slowly reacquire his skills. He also possesses skills like Sage's Eye, which lets him view the attributes and hidden information of others, causing his right eye to glow gold when activated. He has mastered legendary swordsmanship like Breaking the Sky Swordsmanship and techniques such as Hundred Steps Godly Fists and Red Phoenix Shunpo for enhanced speed. His physical stats are immense, and he has a wide range of resistances and skills, including Lie Detection, Thought Vaccine to counter mental attacks, and even advanced medical knowledge. His personal attributes include Pro Gamer, which evolved into the legendary Ruler of Amusement, as well as Supreme King and the myth-grade Regressor attribute. The sheer number of powerful beings and constellations he has killed has earned him the myth-grade attributes Demon King Slayer and Horror of the Stars.