You do not have to be familiar with Overwatch to understand this story as I will weave the necessary information into the story.

For starters, here's the background of Overwatch:

Over thirty years ago, without warning or explanation, a decommissioned set of automated megafactories re-activated themselves and launched a worldwide military campaign against all humanity dubbed the Omnic Crisis. Despite deploying new technologies including powered armour and super-soldier programs, no nation alone could stand against the growing Omnic  army.

It was the United Nations that turned the tide by bringing the best operatives from each nation together to form a strike team. This strike team was both small and nimble and powerful enough to deal devastating blows to the omnics, leading the way for the rest of humanity to fight back. In the end, Overwatch succeeded in ending the catastrophic war and went down in history as heroes.

After the Omnic Crisis, Overwatch experienced a tremendous rise in prominence. For twenty years, Overwatch served as a global peacekeeping force and an engine for innovation, making advances in scientific fields as varied as space exploration, environmental protection, and medical research.

But glory came at a cost. Factors such as controversial missions stoked public outrage, forcing some of the organization’s most famous and celebrated agents to retire in disgrace. Negligence resulting in high-profile mission failures; corruption and mismanagement; weapons proliferation; human rights abuses. Worse still, the existence of Blackwatch a top secret covert operations division within Overwatch - was uncovered.

And finally, the rift growing between the leaders of Overwatch and Blackwatch; Strike-Commander Morrison and Blackwatch Leader Gabriel Reyes climaxed into a skirmish which destroyed their headquarters in Switzerland.

Long story short, the U.N. shut down Overwatch and put the Petras Act into effect. Declaring should any of them take action, they would be considered fighting against the law and punishable by prosecution.

Since, the world has begun to fall toward chaos. Local political leaders have accused certain corporations of using covert operatives to force government officials into accepting exploitative deals and going as far as hiring mercenaries.

The actions of criminal groups have also become more brazen and unrestrained, worse a terrorist organization consisting of the worst of the worst called Talon rose to power in Overwatch's absence.

Worse still, the tensions between humans and omnics that has simmered since the end of the Omnic Crisis have begun to boil over; the assassination of the omnic spiritual leader Tekhartha Mondatta by the Talon agent Widowmaker may have sparked the human-omnic war in Russia known as the Second Omnic Crisis.

Nonetheless, several former agents of Overwatch continued to aid the innocent and deliver justice. Their example has inspired a new generation of unique individuals, including Brazillian DJ Lúcio Correia dos Santos, who used his well-known music to inspire and lead Rio de Janeiro's citizens against the Vishkar Corporation and South Korean professional video gamer Hana Song who employed her skills at the controls of a mech unit to defeat a colossal invading omnic.

And now, one former agent of Overwatch has decided that the time to sit by is over. After foiling the Talon attack on Watchpoint: Gibraltar, Winston, the gorilla scientist who helped usher in Overwatch's golden age, has chosen to defy the Petras Act, by sending his heartfelt message to all former agents, officially reactivating Overwatch.

Source: Overwatch Wikia / Overwatch

A very big thank you to XIII Hearts for being such an awesome editor!

Note:

Characters will interact with each other with their real names. For example, Mercy will be called as Angela. Unless they are on a mission.

Author's disclaimer:

My Little Pony belongs to Hasbro.
Overwatch belongs to Blizzard Entertainment.

I own nothing other than the story itself (if I do own both, I'd be a filthy rich bastud)