Turns out that there's an old Equestrian law on the books that any creature can petition to join any princess's harem. Somepony should have warned Twilight, preferably before the former changeling queen showed up on her doorstep.
After spending Nightmare Night in Ponyville, Luna decides on how to reward the six mares who defeated Nightmare Moon and saved her from herself: Marriage.
In an alternate world, someone could love a thousand different people. When the portal malfunctions, Sunset finds herself stuffed full of memories from her alternate counterparts. Memories of being in love with all of her friends.
Twilight Sparkle arrives in Ponyville to prepare for the Summer Sun Celebration, and potentially the return of Nightmare Moon. All that stands in her way is five stallions who keep flirting with her. Making passes. Hitting on. You get the idea.
Spike spent much of his young life trying to find his place in the world, only to realize it was with those who had become his family. Now, he must decide what to do with new emotions and desires.
Fifteen Year old Spike has found himself attending an academy for girls as part of a co-ed experiment. Will he be accepted or go crazy from hormone overload.
The former human known as Silver has attempted to throw his life away, but neither Luna nor his wife, Night Watch will tolerate this. He claims it was an impulse, but they will cure him of the deep breaks even if it means reassembling him from parts.
Herds. In a world inhabited by magical ponies, that's really not too surprising of a thing... unless that herd consists of four living, breathing goddesses and yourself.
Celestia has made a bet with the current Demon Lord and now the Elements and Spike, led by Princess Luna must face Rias Gremory and her servants in a Rating Game to determine the Strongest Little Sister. High School DxD Crossover.
Celestia and Luna married the mane six, now they have a harem and a honeymoon to deal with. In all honesty, happily ever after isn't all it's cracked up to be. At least there'll be room for orgies.