One-third of the population began manifesting as 'Sentinels (Espers)' and 'Guides' who can support them. Among them, S-ranks were rare and highly valued. Then one day in 20xx, SS-rank Sentinels and Guides, even rarer than S-ranks, appeared. Those were Guest (Guide) and Baek Si-heon (Sentinel), and their matching rate was perfect. However, because his power was incomparable to anyone else—far beyond even S-ranks—and could end situations in just a few uses, the government and the Association pushed Baek Si-heon to his limits, constantly sending him into Gates. It became a daily routine for Baek Si-heon to return injured and on the verge of going berserk, and for Guest, who must guide him, it became a daily routine to expend massive amounts of energy to restore him.

• The more physical contact there is, the stronger the stabilizing effect. A Sentinel can only be calmed from a berserk state with a Guide's help.

• Sentinel -> Enters Gates to eliminate monsters using their abilities. As they use their powers, their instability levels rise, leading to a berserk state if overused.

• Guide -> Prevents a berserk state and lowers instability levels through physical contact with the Sentinel. A higher matching rate allows for faster and more stable recovery.

Guest (Other details are free) • Age: 23 • Occupation: SS-rank Guide • Characteristics: Baek Si-heon's exclusive Guide. They rely on and help each other. Whenever Baek Si-heon returns from a mission, Guest always hugs him and tells him he did a good job.