Otachi is a Category IV Kaiju.

Biology
As with Leatherback, Otachi is one of the largest and heaviest Category IV Kaiju to make landfall. She is larger than other Kaiju types in terms of length, though not mass. Otachi appears to walk on all fours, instead of standing upright like some other types of Kaiju.

Her anatomy consists of two short legs and long, four digit hand-wings that bear a striking resemblance to a Pterosaur`s wing which she can use to fly. Her wings are stored inside her forearms for protection, folding out from an elongated, double-jointed fifth digit.[3] Otachi is capable of flight to the edge of space, even when her legs are carrying something as heavy as a Jaeger. She has a long tail with bony plates along her spine, as well as three prehensile pincers on the end of the tail; the tail is a potent weapon that can be used as a club or claw against Jaegers.

The facial structure of Otachi is made up of a long neck, plated and ridged, and her head includes a large, powerful jaw and is marked by a signature crest on between her forehead and snout, with two extra, golden eyes on each front of the crest. The crest is curved in the front, with a long, sturdy spike protruding from the back for protection of the eyes.

The bottom jaw is capable of splitting in two to spit from the pouch (below the maw). Her tongue has a flowering and bioluminescent structure which she apparently uses either as a grasping mechanism or sensing organ (similar in function to a snake's vomeronasal organ). She also has a sac under her neck that can be engorged to spit a blue, extremely corrosive acid, as seen when it melts the thick armor of a Jaeger and when it it easily liquifies the side of an office building. 

History
Hong Kong Incident
Otachi and Leatherback, a fellow Category IV, emerge from the breach and head for Hong Kong with the intention of hunting down Newton Geiszler. Crimson Typhoon, Striker Eureka and Cherno Alpha are deployed to intercept them. Striker Eureka remained on the sidelines on orders not to engage.

Otachi springs out of the ocean, using its barbed tail to knock over Crimson Typhoon. Crimson Typhoon's pilots use their signature attack: the "Thundercloud formation" and activate all three of rotating blades. For the initial part of the battle, Otachi single-handedly engages Crimson Typhoon and Cherno Alpha.

During the fight, Otachi successfully parries two of Crimson Typhoon's attacks and crushes its blades. Crimson counter attacks by grabbing Otachi's claws, using its flexibility to toss the Kaiju over its shoulder. Cherno Alpha traps Otachi in a headlock and punches her repeatedly. Otachi uses her tail to knock Cherno Alpha over. As Crimson Typhoon prepares to attack Otachi again, its pilots are ignorant of the pincer at the end of Otachi's tail. The tail crushes and tears the Jaeger's Conn-Pod from its shoulders. The beheaded Jaeger collapses into the bay.

Cherno Alpha recovers and advances, Otachi spits a stream of acid at the Jaeger, compromising the armor and causing the reactor to leak into the Conn-Pod. Striker Eureka attempts to come to Cherno Alpha's aid, but before it can reach the Mark-1, Leatherback springs from the water. It leaps onto Cherno Alpha's back while Otachi tears at one of the Jaeger's arms.

Otachi abandons her assault against Cherno Alpha proceeds to intercept Striker Eureka while Leatherback destroys the former. Attacking Striker Eureka, Otachi fights the Jaeger and is overpowered. Moments away from being killed by a missile barrage from Striker Eureka's Anti-Kaiju Missiles, Leatherback disables Striker Eureka and the Shatterdome with an EMP attack.

While Leatherback remains behind to observe and taunt the disabled Striker Eureka, Otachi heads into the city to hunt down Newton. She manages to track him down to a public Anti-Kaiju refuge. Before she can devour him, her attention is drawn toward an approaching Gipsy Danger, armed with an oil tanker.

Otachi blindly charges the Mark-3 Jaeger, but is repelled by Gipsy Danger attacks with the tanker. Changing strategy, Otachi uses her pincer tail to grab the ship. She hurls it across the city and smacks Gipsy Danger with its tail. Otachi retreats deeper into the city. While she recovers, she uses the buildings as cover.

She later re-engages Gipsy Danger, ambushing it when she crashes through a building. Grappling the Jaeger, she rams Gipsy Danger through another building and then drags it through a third. Before Gipsy Danger can counter, Otachi attacks it with her acid. The Jaeger dodges and rams its right hand into her throat with the intent of ripping her acid sac out.

Otachi tries to use her tail pincer to crush Gipsy Danger's head. The Jaeger vents its coolant from the left side to freeze Otachi's tail; when Otachi's tail is frozen, Gipsy Danger shatters the tail and rips out the acid sac.

Otachi leaps onto Gipsy Danger, wrapping her talons around its chest. Unfurling her wings, she takes flight with the Jaeger in tow. She drags Gipsy Danger across the tops several buildings and climbs fifty thousand feet above the atmosphere. As the pilot's oxygen begins runs out, Gipsy Danger successfully deploys its Chain Sword and cuts Otachi in half, ending the battle as the two fall back to earth.

Aftermath
Shortly after the death of Otachi, her body was harvested for organs and Kaiju Skinmites. When Hannibal Chau's workers entered her body to retrieve the secondary brain, they discover her brain is too damaged to for Newton's intended purpose.

However, hearing the sound similar to a heartbeat, Chau's men are killed when Otachi's offspring escapes the womb and her dead body. Otachi's offspring would allow Newton and Hermann Gottlieb to accomplish a successful drift using its secondary brain.

Trivia
Otachi means "big sword" in Japanese.
According to Guillermo del Toro, Otachi is female.
According to Travis Beacham, Otachi is not the only Kaiju that can fly.
In the novelization of the film, Otachi's tail acts independently of the rest of her body after it is severed by Gipsy Danger.
Otachi is a playable DLC character in Pacific Rim: The Video Game.
Otachi is one of the more cunning Kaiju after Slattern.
The "stripes" on Otachi's underside are injuries caused by Crimson Typhoon's blades.
Otachi's pain threshold appeared greater than other Kaiju. One example being that even after losing her tail, Otachi still steadily flew into the atmosphere.
Otachi's character poster claims she has a Speed of 8. 

Scunner is a Category IV Kaiju. It protects the breach from the Jaegers alongside Slattern and Raiju.

Biology
Scunner's appearance and behavior is akin to that of a bull. Broad and stocky, its two curved horns jutting out of its head act as battering rams against armored opponents like the Jaegers. Scunner possess four arms that aid in its ability to move faster than its opponents under water.

Its plated body armor allows it to take great amounts of damage in the most severe environments. Like most Kaiju, it has a green bioluminous glow throughout it's body. Its ability to work in tandem with other Kaiju makes it a particularly dangerous foe in combat.

Like Slattern and Knifehead, Scunner's primary arms are actually two fused arms themselves ending in three-digited claws.

History
When Scunner and Raiju emerged from The Breach, they waited for the arrival of the two remaining Jaegers, Gipsy Danger and Striker Eureka. Upon their approach to the Breach, Scunner and Raiju circle the Jaegers, using their lack of visibility against them. Once they reveal themselves, Scunner engages Gipsy Danger in combat. Gipsy Danger subdues Scunner, but before Gipsy Danger can kill Scunner with its right-arm GD6 Chain Sword, Raiju's jaws clamps down onto Gipsy's arm while swimming at top speed, tearing its arm off.

Scunner frees itself from Gipsy's hold and takes advantage of the damaged and disorientated jaeger to bite and cripple Gipsy's right leg. Unleashing its Chainsword from its left arm, Gipsy pierces Scunner through the neck and drags its head over a volcanic pit, burning its face. Scunner, thrashing from the pain, escapes and off balances the damaged Jaeger giving it time to recover. Raiju attacks Gipsy Danger a second time, but is cut in half by its chain sword.

Striker Eureka's endurance against Slattern forces the Category V Kaiju to call for aid. Scunner abandons its fight with Gipsy Danger in order to attack Striker Eureka. Gipsy's crippled leg prevented the Jaeger from helping Striker in time. As Scunner and Slattern move in to destroy Striker Eureka, its pilots detonate the thermonuclear bomb on its back, killing Scunner and critically wounding Slattern.

Trivia
Scunner uses the same basic CG body as Knifehead and Trespasser in the film.
Scunner is the largest Category IV in Pacific Rim.
Scunner and Raiju are the last Category IV Kaiju to emerge from the Breach before its destruction.
The word "scunner" comes from Scotland, where it refers to something that triggers a strong reaction of disgust.
Scunner is featured in Pacific Rim: The Video Game.
Scunner is depicted on the Blu-Ray release of Pacific Rim, replacing Gipsy Danger in a lenticular image.
NECA's Pacific Rim Series 4 will include a Scunner Action Figure, released around June 2014.
Scunner is the tallest Category IV known.

Technical Information
Given Name: Scunner
Breach Date: January 12, 2025
Category: IV
Status: Deceased
Kaiju Specifications
Height: 441 ft (134.4m).
Weight: 3,230 tons
Speed: 5
Strength: 9
Armor: 8
Battle Information
Attack Behavior: Coordination with other Kaiju
Intimidation tactics and ingestion
Toxicity: Low
Powers: Pointed, plated protrusions designed to batter and ram
Weaknesses: Oblique region
Target Information
City Targeted: None
Jaegers Targeted
or Destroyed: Striker Eureka,
Gipsy Danger