The Speed Monster's former human identity is almost entirely unknown. It is known that he was a resident of room 705 in the apartment and that he dreamed of being a track and field star. The original human also appeared to be extremely envious of others and amoral; he killed his friend out of jealousy of his track and field skills.
The Speed Monster takes on a generally well-toned, humanoid appearance. However, its head is somewhat elongated and it possess a large third eye in the center of its forehead. It appears to be sadistic and retains its former human self's amorailty as it was willing to use Yuri Park to prevent Wook Pyeon from throwing lighter fluid at it. It also enjoys a good challenge, noting to itself that fighting Hyun, who managed to harm it, would be fun, and taunted Wook over his lack of speed.
As the name implies, the Speed Monster is incredibly fast; its powers based on the desire of being a track and field star. It uses its speed to add force to its attacks. However, it cannot maintain its fast speed forever. After each sprint, its skin changes from gray to a reddish hue, in which it moves slower. It is able to recover quickly, but this provided a small opening to try to kill it.
Hyun Cha, Wook Pyeon, Yuri Park, and Mr. Ahn first encounter the Speed Monster in a stairwell. Hyun was taken aback by how his phone did not detect the monster, but noticed it was sleeping. The party attempted to pass by it quietly. Hyun and Mr. Ahn successfully get to the next floor, but when Yuri passes by, she hears her phone beep, and then turns to see the monster has woken up and is staring right at her. The monster attempts to strangle her, holding her in between itself and Wook, and then quickly moves to attack Wook, knocking the two unconcious.
Hyun attempts to fight the monster, but its speed proves too great to react to. However, Hyun notices its color change and realizes the reddish hue means it has to recover and will move slower for a few moments. This lets Hyun attempt to douse it, but could only catch its foot on fire, which let the monster snuff it out. The monster gets excited over this challenge. Eventually, Hyun manages to trap it and use his electric spear to stun it. It was eventually incinerated.