Terraside 1

* Title screen
* Original title card

**Terraside 1** is the fourth episode of Mainstream and depicts the Replacer Syndicate launch their attempt to see their ultimate goal through: the completion of Project Terraside.

## Synopsis

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> *Operation Terraside, commence. In the midst of global chaos caused by Replacer Syndicate's schemes, Yoo Mina is confronted by an unexpected individual.*
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## Appearances

* Coffin Company
	+ Managerial Department
		- Machine G.A.P.
		- Lee Sooyeon
		- Kim Hana
	+ Operation Department
		- Lena Mackenzie
		- Chloe Starseeker
	+ Fenrir Squad
		- Yoo Mina
		- Joo Shiyoon
		- Hilde
	+ ALT Squad
		- Seo Yoon
		- Xiao Lin
		- Eujin
		- Kim Sobin
* Replacer Syndicate
	+ Replacer King
	+ Replacer Queen
	+ Regenerated Knight
	+ Replacer Knight (Mentioned only)
	+ Regenerated Bishop
	+ Replacer Bishop (Mentioned only)
	+ Project Terraside
	+ New Ohio
* Ian Mason (Mentioned only)
* Jane Doe
* SWAT 4
	+ Kang Soyoung
	+ Lee Yumi
	+ Park (Mentioned only)
	+ Bona (Mentioned only)
* Magellan's Prediction Society
	+ Magellan
* Delta Seven
	+ Maria Antonov (Mentioned only)
	+ Sylvia Cooper
	+ Kyle Wong
	+ Freedom Strike
* Mason Mercenary Office
	+ John Mason
* Six Wings
	+ Na Yubin (Mentioned only)

## Plot Summary

### Act 1

Jane Doe is seen evading Replacer troops in one of their hideouts. Replacer Queen catches up with Jane; Jane tries to shoot her, but her shots are not effective. Queen urges Jane to surrender, but Jane refuses. Queen then mentions that she wouldn't have had Ian Mason killed if she knew Jane would be this much trouble. Queen orders her troops to kill Jane, but she escapes through a window. Replacer King orders the troops to not pursue. With the immediate situation handled, King tells Queen that it is time to move towards the Replacers' true goal: Executing Project Terraside.

Meanwhile, at Coffin HQ, Hilde and Shiyoon notice that Mina is taking an excessive number of jobs, cutting into her health. After going out on another job, the mercenaries she was working with complain that she was rushing ahead and nearly getting them all killed. When she returns to HQ, Sooyeon orders Mina to go to an amusement park with Shiyoon, hoping that Shiyoon will be able to mend Mina's behavior.

At the park, Mina tries to leave almost immediately but Shiyoon says that Sooyeon will fire her if she leaves before the park closes. After Shiyoon is unable to interest Mina is the park activities, he starts a game of truth or dare. He asks Mina about her parents, mentioning that he was able to find information about her and her sister but nothing about her other family members. Mina angrily tells him not to pry into her personal life beforein turn asking him about his parents instead; he says they were murdered but, before he could elaborate, the two see a ship crash into the park. As C.O.s appear around the ship, Mina rushes out to fight them.

As Mina focuses on the C.O.s, Shiyoon claims Mina of having PTSD for what occurred to Replacer Bishop; Mina denies this at first but passively concedes. The two notice that the other visitors in the park are suffering from Corruption Syndrome; that should only be possible at CSE Level 4 and up. Shiyoon notes that the C.O.s are protecting the ship that smashed into the ground, so Mina decides to rush forward and destroy it. After doing so, the police evacuate the civilians nearby and thank Shiyoon and Mina for their help. However, they then notice that the ship is regenerating.

Shiyoon proposes the two run away due to them not being legally allowed to continue assisting in another TASKFORCE's jurisdiction (outside of self-defense). Mina only agrees when Shiyoon mentions that no money can be made from the situation until Regenerated Knight appears. Knight attacks, but the two are able to defend themselves. Knight is willing to do another round of fighting until Regenerated Bishop tells Knight to stop, and the two Replacers leave to install the next Terraside Terminal. Mina is in shock at Bishop's return.

### Act 2

Mina and Shiyoon meet up with Hilde and Sooyeon on the Coffin; Sooyeon reports that the Administration has officially issued a global emergency alert as the Terraside Terminals - otherwise known as the Lost Ships - have appeared all over the world and apparently causing acute Corruption Syndrome in surrounding people. The Lost Ships appear unable to be completely destroyed, so the Administration is forced to constantly destroy the ships to keep their effects contained while fending off Replacer troops. Mina asks if Coffin will be assisting the Administration in destroying the ships, but Sooyeon denies it; instead, they will be accepting a request from a client who may be able to defeat the Replacers.

After Fenrir Squad reaches the rendezvous point, Shiyoon and Hilde discuss how the Replacers could have brought their officers back from the dead. Lee Yumi and Kang Soyoung of SWAT 4 are attacked while on their way to the rendezvous point by Magellan's Prediction Society. Once Fenrir Squad defeats Magellan's forces, Fenrir Squad take SWAT 4 into the Coffin, and SWAT 4 puts the others in contact with their client, Sylvia.

Sylvia explains the Lost Ships are getting stronger each time they are destroyed, necessitating a permanent solution. She also informs Hilde that Delta Seven expended a great effort to get the intel Hilde requested before Kyle Wong ends their communication in a hurry to handle a Lost Ship in New York. Soyoung then provides the intel and informs the others of Elixir, a drug that enables rapid regeneration from fatal wounds. She says Magellan's Prediction Society is responsible for the drug's production and distribution, so the group then goes to the Society's headquarters.

During the raid on the Society's headquarters, Knight and Bishop are speaking inside. Knight reports she has gathered enough Replacer Factor to power the Terraside System Core, so Bishop orders Knight to leave. Magellan enters, panicked over the attack, and requests a vial of Progressive Factor. He takes some and mutates into a Replacer collapser. Magellan rushes outside, where he is killed by Fenrir Squad and SWAT 4. While Fenrir Squad is dismayed that their only lead has died, Bishop reveals herself and admits that she caused Magellan's mutation. While the group expects a fight, Bishop instead surrenders. Hilde decides to imprison Bishop inside the Coffin and brings SWAT 4 along at their request.

### Act 3

Hilde begins interrogating Bishop, barring Mina from meeting with Bishop instead. Bishop offers to give any information on the Replacers Hilde is looking for in exchange for meeting with Mina, but Hilde refuses. Hilde mentions she already knows that the Replacers are using a revised version of the Old Administration's Immortal System, a reality interference technology, and that the Replacers have been spreading Elixir so that Replacer Factor can be mass produced in users' bodies. Bishop is initially shocked that Hilde knew so much but follows up with asking why Hilde is watching Mina closely. Hilde does not respond and leaves the room. Shiyoon, who had been eavesdropping, asks her as to why she's spared Mina unlike others who used Qliphoth Factor, but Hilde refuses to answer. Before Shiyoon can continue, they are interrupted by a Replacer boarding party seeking to find Bishop.

Meanwhile, at Coffin HQ, Sylvia commends Coffin Company for capturing a Replacer officer and makes her way to them so she can transfer Bishop into American custody. ALT Squad reports to Sooyeon, who informs them that they will switch out with Fenrir Squad to keep Bishop secure until Sylvia arrives. As Sooyeon calls the Coffin, she finds out that the ship is under attack; Sooyeon changes ALT Squad's orders to preventing Bishop's rescue instead. The Replacers manage to find Bishop and attempt to execute Bishop. Bishop is shot, but the Replacer strike team retreats when Mina arrives to help.

On the ground, Eujin finds Seo Yoon in a call with someone; Yoon ends the call in a hurry. ALT Squad meets up with Soyoung, and Soyoung asks who Yoon was talking to. Yoon says she was talking to a psychiatrist, whom she claims to be seeing due to her previous abduction by Bishop. She says that if she handles the mission well, her psychiatrist will declare her cured of any trauma Bishop caused.

Back on the Coffin, Hilde mentions that Bishop is injured and placed in the ICU, so Sylvia demands that Bishop be interrogated before she dies. Shiyoon mentions that Bishop did make an offer to give information, and Sylvia orders Coffin Company to agree to the deal as long as the Replacer hideout can be found. As Bishop requested, Mina meets with Bishop as Shiyoon watches. At Bishop's request, Mina and Bishop join hands, and Bishop says she'll give the location of the Replacer HQ in four hours — holding hands with Mina for that amount of time will be enough to decode the location of the base as the decoding key requires both Progressive and Qliphoth Factors.

Coffin personnel are forced to deal with another Replacer attack when multiple Replacer ships surface from the Counterside, forcing the Coffin to dive into the Counterside to evade the ships. In the ICU, Bishop offers to tell Mina what the original Bishop thought before she died, but Mina refuses, saying Regenerated Bishop is a walking corpse.

ALT Squad and SWAT 4 arrive at the Coffin's location. The Coffin lands so they can board, but Knight leads a force of Replacers to attack the ship shortly afterwards. Soyoung looks into the ship's navigational log and finds that Yoon gave the Coffin's location to the Replacers. Hilde exits the ship to face Knight, but Queen arrives to reinforce the Replacers. Lin moves into the ship to protect Mina, who is still decoding with Bishop. The Replacers attempt to break into the ship, so Mina moves Bishop away from the ICU as Lin provides cover fire. When the three enter the hallway, SWAT 4 arrives to help Lin.

As the group fights off various Replacer troops, Queen arrives to take Bishop back. Yoon also appears; Lin initially thinks Yoon has arrived to help, but Yoon reveals that she's defected to the Replacers as she's tired of being treated as a weakling as ALT Squad's leader. Queen confirms that she'll give Yoon Replacer Factor so she may become stronger, and then Bishop reveals that she retrieved the necessary Qliphoth Factor to repair the Immortal System Core. Realizing how strong Queen is, the group allows Queen, Bishop, and Yoon to leave but not before Bishop tells Mina to check her email.

### Act 4

Back at Coffin HQ, Sooyeon receives news about the events on the Coffin, noting that everything is going as the Administrator predicted. The Administrator, now revealing himself, explains that he is building up events such that the desired outcome cannot be prevented.

On the Coffin, Sylvia and Kyle arrive to retrieve Bishop but discovere that she is gone. Kyle admonishes Sylvia for her apparent laziness and is about to leave to report her to the Lieutenant General when Mina gives Sylvia the data she got from Bishop through her email. Sylvia is overjoyed when she discovers Bishop sent the Replacer HQ's dive coordinates. She urges for an attack on the HQ right away because the coordinates are single-use as it utilizes a Schrodinger-Type Quantum tunnel— thus, there is no telling when the path to the HQ will close. ALT Squad is ordered to return to HQ by Hilde as the commander thinks they are untrustworthy.

Upon completing the dive, Sylvia further analyzes Bishop's data and finds out about the System Terraside, a reverse terraforming system that turns reality into an environment similar to the Counterside. She states that the group must destroy the system, which is composed of the Immortal System and the Replacer Factor Transmission Sytem— the Immortal System is responsible for the Lost Ship regeneration, so its destruction would disable the Lost Ships. The Replacer Factor Transmitter, on the other hand, is responsible for spreading Replacer Factor contamination throughout the world. However, Sylvia says that the Replacer Factor Transmitter must be destroyed first so the Immortal System can be found due to the latter component's innate stealth capabilities.

After a short search, Kyle spots the Replacer Factor Transmitter. Regrouping at the ship, Kyle and Sylvia say that they will lure the Replacers out while Fenrir Squad and SWAT 4 use different routes to reach and destroy the transmitter. When the transmitter is destroyed, Sylvia reports that the Lost Ship regeneration has slowed down and the areas causing Corruption Syndrome are dissipating in Normalside. A structure believed to be the Immortal System Core appears nearby, but Yoon, now empowered with a combination of the Progressive and Alternative Factors, arrives to stop the team from destroying it.

Fenrir Squad questions Yoon as to why she defected. Yoon claims she and the Replacers have a mutual interest to work together despite their apparent and previous hostilities. She sends a force of Replacers after the team, saying she'll fight the group herself if they manage to reach the Immortal System. After the Replacer force is defeated, Kyle asks Lena for more supplies, but Lena says they are nearly out of resources. Hilde orders the group to push forward regardless, and they again encounter Yoon along with a horde of Replacer Pawn splitters. The team manages to break the Force Barrier protecting the Immortal System Core, and Sylvia has Kyle call in the Freedom Strike fleet, though Kyle felt their arrival would be impossible due to the dive coordinates. The coalition fleet consisting of Stiletto, Skeleton Eye, and Blue Bridge nevertheless manages to arrive thanks to Sylvia providing them with the quantum tunnel's previous coordinates. The fleet bombards the Immortal System Core, destroying it.

Kyle reports that the Lost Ships stopped regenerating, but Soyoung is suspicious due to the other Replacer officers not showing up to protect the Immortal System Core. Replacer Queen arrives to assist Yoon, incapacitates Shiyoon and announces that the Syndicate just managed to finish building a second Immortal System Core. The core is then used to destroy the Freedom Strike fleet and damages the Coffin enough to force an emergency landing order. Queen reveals that the second Core is not only fueled by the Qliphoth Factor, providing it with near-infinite energy, but is also mobile as it is placed on a dimensional ship. Sylvia and Kyle are shocked when they realized the core is being carried by the New Ohio, Delta Seven's flagship cruiser that went missing years ago. Even more, the Replacer King also appears on comm and reveals himself to be Dominic King Reginald, former Brigadier General and Deputy Commander of Delta Seven who also went missing at the same as the ship. Replacer King has the New Ohio dive again, taking the Immortal System Core with it.

Back in Normalside, Mina meets with Shiyoon in the hospital. She explains that Kyle and Sylvia returned to Normalside to help against the Lost Ships, which have begun regenerating again. Hilde was specifically summoned by the Administration to assist them, and the damage to the Coffin made future missions nearly impossible. SWAT 4 bursts in and says they will help fight the Replacers. John Mason also appears and says he has a way to defeat the Replacers despite their grim chances.

## Gallery

King orders Queen to not pursue JaneTerraside Terminals crash into the amusement parkBishop provides Magellan with ElixirShiyoon confronts HildeMina and Bishop holding handsThe Freedom Strike fleet arrives to destroy the system coreThe New Ohio appears