Pinkie Pie is born to make people smile. It's in her nature.

So after a few strange beings ended up in Equestria, and she got to know Shadow - the serene and lonely Hedgehog - she immediately began trying to make him happy. But so far, it hasn't been working. She's tried everything, but he just doesn't seem to be a sociable guy.

She has already learnt her lesson, thanks to Cranky Doodle. She can't just pester Shadow in an attempt to make him crack a grin. Instead, she has to find out what had turned him into such an introvert. So she decides to throw him a huge, blowout surprise party for him on Hearts and Hooves day.

But she has barely scratched the surface of Shadow's dark history. Little does she know of the things in store for her that particular Hearts and Hooves.

She is Loyalty. She will be the last one standing by her friends, in peril, torture and death.

This is what everyone believes. This is what Twilight and the other Spirits of Harmony, Rainbow's friends, believe. And they took it entirely for granted. After the Mare-do-well incident, Rainbow Dash's Loyalty began to falter. She still felt the terrible sorrow of being deserted by everypony, to be forgotten in the shadow of a greater hero.

Over time sorrow grew to anger. As the powerful bond of friendship crumbles as Rainbow begins to drift away, The others discover just how powerful the Element of Loyalty is, and how its absence might have caused the downfall of the greatest heroes Equestria has ever known.

After his so-called reformation, Discord longs for revenge on the Spirits of Harmony. So when he is visited by Dr. Eggman, offering revenge on his enemies in exchange for partnership, he jumps at the chance. Now the heroes from both worlds work together to bring both villains down as they try to collect all the chaos emeralds... and destroy the Elements of Harmony once and for all.

But maybe fate brought these two worlds together for a greater reason. Each Spirit of Harmony has a bond with one of the Sonic Heroes, the greatest of all between Sonic and Rainbow Dash. With both Chaos Control and Friendship, both worlds combined would be unstoppable. Unfortunately, the same may be said for the enemy.

This is the constant struggle between Chaos and Harmony opened up to a whole new level.