Mercy was an Imulsion township that mined, refined, and sold Imulsion throughout the Pendulum Wars, and was the site of a large bombardment by the Union of Independent Republics. Mercy survived, and continued to do so after the Locust Horde emerged and attacked every major city on Sera shortly after the end of the Pendulum Wars. One year after Emergence Day, the newly elected Chairman Richard Prescott ordered all cities outside the Jacinto Plateau to be incinerated by the Hammer of Dawn. Mercy was spared, but the neighboring city of Char was hit. Afterwards, Mercy was abandoned by the Coalition and occupied by the Stranded, survivors of the Hammer strikes, who continued to use Mercy as an Imulsion pumping station. However, the city became overrun by the Lambent in 17 A.E. during the Lambent Pandemic, turning most of the citizens into Lambent Humans. In Bloom, 17 A.E., Pvt. Dominic Santiago, in a sacrificial attempt to save his squad mates during the Mission to Mercy, destroyed the Imulsion station to kill the Locust and Lambent forces so that his comrades could escape. Despite this destruction, most of the city was still standing by 42 A.E.
The area that would become Mercy contained a large reserve of natural Imulsion, as did the surrounding areas of Char and Concord. Mercy first became settled as an Imulsion mining colony and ultimately an incorporated municipality in 150 B.E.
During the history of Mercy, the Flores Family became a prominent family name in Mercy. At a certain point, the Flores Family constructed their own family graveyard.
In 79 B.E., the Union of Independent Republics, a collection of nations economically and politically bankrupt due to the lack of Imulsion reserves, waged the Pendulum Wars against the nations of the Coalition of Ordered Governments that had the majority of Imulsion reserves and became the political and economic superpower of Sera.
Due to being one of the places within the nation of Tyrus with a large Imulsion reserve, Mercy was often the target of possible attacks by the UIR, resulting in numerous bomb shelters being built throughout the town. In 9 B.E., the UIR attacked Mercy with mortar strikes. Although the city still survived, the town square was destroyed and the people devastated. Mercy rebuilt by the people still were affected by the attack.
The Pendulum Wars came to an end after 79 years of conflict, but six weeks after, a race of subterranean species called the Locust Horde emerged and attacked every major city on Sera in an attempt to slaughter every human on the surface in what would be known as Emergence Day. On Emergence Day, the city was evacuated. However, it was largely unaffected by this initial attack.
However, the Flores Family was heavily affected. Mr. and Mrs. Flores, and their grandchildren, Benedicto and Sylvia Santiago were killed by the Locust on E-Day. While unable to bury the children, Maria Flores-Santiago buried Mr. and Mrs. Flores in the Flores Graveyard in Mercy.
One year later, the Coalition ordered every major city to be destroyed by the Hammer of Dawn. Mercy was one of the few cities spared, but its neighboring city of Char below was destroyed. The survivors of the Hammer strikes who rejected the COG for sacrificing its civilians, the Stranded, took over Mercy and continued to mine, refine, and sell Imulsion for those in need, retrofitting a large Imulsion pipeline straight from the refinery to the Imulsion pumping station at the entrance of town.
- "STAY OUT!
NOT SAFE FOR HUMANS!! any actual people (not un-people) coming to Mercy should STAY AWAY because there is something really weird going on like some kind of CRAY FEVER or SOME OTHER CRAP and I'm likely to SHOOT YOU if I can't tell you apart from those sickass freaks!
They're not gonna stop unless I stop them!!!!"
- — A warning letter about the pandemic posted in Mercy.
Two years after the sinking of Jacinto, the town of Mercy became a major area of activity for refugees who came to rely on its primary Imulsion pumping station for resupply. However, in 17 A.E. its Stranded population faced an epidemic that was worse than Rust Lung. Serans in the town began falling ill with symptoms including fever and muscle pains. As the epidemic began to spread, the citizens of Mercy tried to fight it by boarding up the homes of the ill to keep it isolated, but it failed. In just a few short months, most of the town was affected, except for a few survivors, including one crazy old man who rigged the pipeline running through the town with explosive charges. He believed it was the Imulsion causing the epidemic, and wanted to keep it from spreading.
Delta Squad arrived in search of fuel for their trip to Azura, but found the town deserted and the fuel pump shut off. They followed the pipeline to find the fuel pump, and discovered the charges placed on the line. After deactivating the third charge, the crazy old man shot at Delta Squad and warned them about the 'fever' before running away. They soon discovered that the crazy old man had died, not by Locust but by a Former, a human who has turned Lambent. Swarms of them packed the area, and Delta Squad was surrounded, but they pushed their way towards the town hall, only to find themselves blocked. Swarms of Formers begin to attack them, and a Stranded on the balcony above them informs Delta to get on the machine gun to fend off the Formers. After defeating the wave of Formers, Delta Squad joins the Stranded inside, but before they can ask anything more than how the Lambency starts, more Formers ambushed everyone inside. The Stranded are immediately killed, and Delta Squad pushed through the Formers to the church, where they discovered the fuel pump. As the rest of Delta activated the pipeline, Dom visited his family's grave and left his COG tag along with Maria's necklace there. The pipeline was successfully activated, but the tanker was too heavily damaged to hold the Imulsion, forcing Delta to abandon their plan. They got back to Dizzy and Jace but were ambushed by the Savage Locust, and then the Lambent came to join the fight. Delta fought them off until Dom sacrificed himself by driving a truck into the tanker, detonating the Imulsion and destroying the enemy forces.
The attack left much of the deserted city destroyed, and its Imulsion pumping station rendered inoperable. The remaining Lambent and Locust infesting the city and its surrounding areas soon after were wiped out by the activation of Adam Fenix's Imulsion Countermeasure Weapon.
- Gears of War 3 Collectible-Panicked Letter.