Orthrus is a two-headed juvenile gate guardian and the former pet of Geyrun, a son of the fire god Emberus. He was drawn into the Nothing on the day Geyrun was murdered. When Carl and his companions inadvertently release him onto the Fifth Floor, his enormous size endangers a bubble world even though he behaves like an excited puppy. His survival becomes the object of one quest while a second quest offers every crawler a reward for killing him. Carl and Donut eventually bring him within Emberus's reach, ending the immediate danger; the System then reports that Orthrus is on the Twelfth Floor.
Geyrun's missing puppy
Orthrus belonged to Geyrun before Geyrun's death. The description Carl receives on encountering the animal identifies him as Geyrun's bereft pet, calls him a level 10 juvenile gate guardian, and names Cerberus as his older brother. Cerberus is associated with guarding a stairwell exit on the Twelfth Floor; Orthrus had been intended for a similar role but had not completed that development when he lost his master. His two heads and gate guardian classification describe what he is, while his behavior on the Fifth Floor shows how young he remains.
Geyrun's murder and Orthrus's disappearance happened on the same day. Samantha tells Carl that the puppy was sucked into the Nothing accidentally. She also explains why Emberus is searching so aggressively: Geyrun was the son for whom Emberus had particular affection, and Orthrus was his missing dog. Emberus is blind after removing his own eyes in grief. His search therefore does not proceed by simply spotting the immense puppy elsewhere among the bubbles. When a dog soldier crawler catches his attention, he mistakes her for Orthrus and pounds on the wall of her bubble, heating the world inside it.
The System's description says that Orthrus has escaped the blight that usually affects creatures touched by the Nothing, attributing this exception to his innocence. It also describes him as immune to fire, a useful protection near Emberus. Neither protection makes him invulnerable to other injury. His listed level is low beside the divine beings around him, and the events of the Fifth Floor repeatedly show that ordinary attacks and environmental hazards can bring his health close to zero.
A giant inside bubble 543
Orthrus appears inside Carl's Fifth Floor bubble after the group's encounter with the Gate of the Feral Gods. At first, Carl does not recognize the scale of the presence registered on his map. The puppy occupies nearly half the bubble's available space. His legs stand in the water while his belly presses against the side of the necropolis, dislodging stone. A small hop shakes the landscape, sends a wave across the area, and brings down a stone statue onto a pazuzu hut. These effects arise from an animal struggling to move in an enclosure far too small for him, rather than from an attack on the crawlers.
The bubble is already facing a storm and an unfinished quadrant battle. Carl's group wants to open its stairwells, but the plan for defeating the temple's boss involves conducting lightning through the structure and its waterways. With Orthrus standing in the water, that tactic could hurt him too. He is also being bitten by sharks around his legs. The System announces his suffering to the floor and warns that, if he dies, Emberus will burn the bubble. Carl recognizes that allowing the puppy to die would endanger people who have no control over either the god or the rescue plan.
The danger becomes immediate when the bubble's lightning attack proceeds. Orthrus's health almost falls to zero. Donut heals him, but the continuing shark bites keep draining his health. The opening of bubble 543 removes the enclosed world's roof and gives him a path out into the surrounding lacuna; it does not by itself make him safe. Carl still has to get the vulnerable puppy away from the water and across the spaces between bubbles to Emberus. The partial bowl left by Orthrus's passage remains a feature of the group's later evacuation plans.
Bringing Orthrus across the lacuna
Carl and Donut use the Drop Bear, a biplane carried with Louis and Firas's flying house, to reach Orthrus. Katia works on the aircraft before takeoff, while Louis and Firas lift the house high enough for Carl to launch the plane from it. The improvised flight matters because Donut must get close enough to heal the puppy, and Carl must then move faster than an animal large enough to leap across the Fifth Floor's bubble worlds. The pilot has little room for error: an abrupt maneuver could wreck the plane, and a playful movement from Orthrus could crush it.
Donut restores his health during the flight. The pair then use a scroll of Meat Hooks to attract him. The spell produces a foul trail of black smoke from Donut's paw that appeals to pets. Orthrus follows the aircraft, although he continues chasing after the spell is no longer close enough to compel him. He bounds over intact bubbles, slips on their surfaces, and resumes pursuit whenever the plane catches his attention. At one point he paws at the smoke above Carl and Donut. He appears to be trying to catch what interests him, with no evident awareness that the aircraft and its passengers could be destroyed by a single swipe.
His movement nevertheless damages the inhabited worlds below. A world quest announcement reports that he has drenched the people in bubble 331 and knocked down the Sounder Tower in bubble 298. Carl's party also sees him tumble across the lacuna's mixture of intact and opened bubbles. Orthrus's size makes a normal puppy's curiosity consequential on the scale of whole settlements. Guiding him is therefore more than keeping him alive: every diversion or fall may put other crawlers and residents in the path of his body.
Two opposed quests
The first quest, The Dumber of the Flunkies, obliges surviving participants from an earlier group quest and the crawlers in bubble 18 to reunite Orthrus with Emberus. Emberus believes the puppy is inside bubble 18, where his search is putting the occupants at risk, but Orthrus is outside bubble 543. The quest offers a platinum quest box for bringing them together. It also warns that harm to Orthrus means failure and that Emberus will then pursue the participants across floors. The obligation is imposed on the affected crawlers; they cannot opt out of the group quest.
The System then broadcasts a second quest, Get Orthrus, to all living Fifth Floor crawlers. Despite its name, its object is to kill the puppy before he reaches Emberus. The offered prize includes gold, level-up potions, and a pet monkey. The announcement even extends the reward to crawlers already charged with protecting Orthrus. In practical terms, it makes the protective party responsible for keeping a fragile target alive while inviting unrelated crawlers to attack him. Katia and Elle warn other groups against striking the puppy, but the reward is large enough to draw pursuers anyway.
Orthrus has no part in choosing either objective. He is a quest target because of who owned him, where he has appeared, and what Emberus will do if he dies. The two quests turn his rescue into a conflict among crawlers even though the puppy himself is not hunting them. His level 10 designation does not measure the risk that killing him would bring from a much more powerful god, nor does it account for the damage his size can cause while he is alive.
Attacks during the rescue
Quan Ch is the most persistent of the crawlers pursuing the kill reward. He attacks Orthrus from the air, driving the puppy's health down while Carl and Donut turn the plane back to intervene. The dog cowers between bubbles with his ears flattened and his health at about one fifth of its maximum. Donut's magic missiles strike Quan, but his shield protects him. Carl attacks him from the plane's wing with a thrown explosive, disrupting his assault long enough for Donut to heal Orthrus. The restored puppy immediately becomes interested in the aircraft again, so the rescuers must return to leading him toward Emberus rather than simply stopping to guard him.
Other attackers complicate the route. A fish-shaped airship fires harpoons toward Orthrus; the shots fall short, and he collides with the vessel without apparently noticing it. Closer to Emberus, crawlers on the floor of the lacuna launch spells at the puppy. A fireball has no effect because of his resistance to fire, but the attack shows that the competing quest is still attracting participants. Orthrus bounds away from one group, then slips across a popped quadrant. He is moving through a battlefield he does not understand, while Carl and Donut have to watch for threats from above, below, and behind.
Quan returns and strikes Orthrus again. The puppy collapses with only two percent health and a one-minute unconsciousness timer. Donut heals him while the Drop Bear loses control and begins to fall. A temporary period of invulnerability protects Orthrus from further attacks, but Carl sees both Quan and a group on the ground poised to resume as soon as it expires. Healing has removed the immediate danger of death; it has not resolved the pursuit, the failing aircraft, or Emberus's continued search at the wrong bubble.
Reunion with Emberus
With the plane spiraling and the attackers closing in, Carl invokes Emberus through the dungeon's worship system. The intervention brings the god to Carl's position in a different, immense form. Carl gains temporary protection, but Donut does not share that protection. The Drop Bear strikes the manifested god and is destroyed. The maneuver finally brings Emberus close enough to recognize the puppy he has been seeking.
Emberus responds to Orthrus with relief rather than hostility. Orthrus disappears before the intervention's allotted time ends, and Emberus vanishes immediately afterward. The System subsequently announces that Get Orthrus has failed because no crawler killed the level 10 puppy, while The Dumber of the Flunkies has succeeded because he was saved. Its completion message places Orthrus on the Twelfth Floor, where he is to resume gate guardian training. That is a firmer account of his immediate destination than the earlier quest's promise that reunion would send both him and Emberus back to the Celestial Halls.
The reunion closes the Fifth Floor emergency without closing Geyrun's murder. Later, Carl describes Orthrus as the two-headed puppy released from the Nothing and identifies Geyrun as his murdered owner. Carl's separate obligations to Emberus concern finding Geyrun's killer and dealing with Hellik, a suspect whose apparent alibi complicates the accusation. Samantha also remembers Orthrus when Carl asks about Geyrun. These later references preserve the connection between the puppy and the unresolved death, but they do not give Orthrus a new on-page role in the investigation.