Equestria had already gone through a timultous time with the nececity of the conversion bureau, but nopony saw the Day of Fire comming; some say it was God's wrath for the hubris of ponykind's involvement in destroying the human race.
When Jen rebuffs Douglas Reynholm's advances saying that she'd be with him when her entire department got ponies, but not just any ponies, talking ponies he turns to the only thing that can possibly help: Spaceology's “Spacestar
Lyra's always wished to meet a human, and Discord's looking to stir up a little excitement [he's REFORMED, not boring] — so he grants her wish and summons a cursed ninja; that's be worth some excitement, right?