Jason Wright is dead. The Elements and all of Ponyville are to blame for his abuse for three long horrendous years. Princess Celestia, upon hearing about this, lays down righteous judgement on each of them. This breaks their friendship and causes them to scatter to the winds while also destroying the reputation of Ponyville itself.
Two years later, a second human enters Equestria for a job. He and his new companions are a part of a mercenary team, not well known, but unique in their own way. Little does this human know that a simple job his team accepted in Equestria will lead him to becoming involved in something bigger.
EDIT: Changed setting to Teen, but may change it back if things get a bit too dark.