Twilight and Starlight, and Celestia and Luna, are called on a friendship mission to the land of Biquestria, which is just like Equestria, but it's populated by relatives of ponies known as Bicorns, unicorns with two horns, where the Lodgers are conveniently to help Pang Bing with Equinox magic. Starswirl is actually pleased that his surrogate daughters actually get a friendship mission and so does their actual parents, but he immediately recognizes the friendship problem right away. So he convinces the map to let him tag along as it's creator, and he discovers he was right as it is from it's very own leaders Prince Major Pulse and Prince Minor Pulse, two brothers just like the previously hard relationship of Celestia and Luna. On his travels after the reformation of Stygian, Starswirl met them and discovered they co-rule the land since the passing of King Pulsar, but they initially went into a cursed lifestyle as they ran both the neverending magical pools that they developed to tap into the energy they access from both their horns: positive (light) and negative (dark) magic, and while Minor ran the negative pool and thus became hated and shunned in absolute, Major ran the positive pool and was praised and adored in absolute, in a similar fashion to the story in Rainbow Dash Presents A Star in Yellow. Because they were unable to balance themselves out with the two energies, they were cursed with praise or scorn, resulting in a series of arguments, misunderstandings, inferiority and superiority complexes, jealousy, anger, rage, egotism, and so on. This ended at last when Minor Pulse, after having drawn the line when he was treated so cruel by his subjects, destroyed himself with a raging argument with Major, turning him into Majes Minor, a Nightmare Moon-like menace who destroyed Major's social life successfully and took joy in seeing how it felt to be in his horseshoes, and after a massive fight, Major had to acknowledge reality and tap into the negative magic, knew when to draw the line, and banished Minor into the magic pool he controlled. By taking his old role as the watcher of the negative pool, he fully recovered from the positivity curse, and saw the errors of his ways, and swore to heal Minor. He eventually does so with help from a bicorn filly protégé named Parhelion Glow and 4 other friends, Nebulus, Stella Wind, Cosmo Horns, and Aster Space, and after saving Minor Pulse from the negativity curse and reuniting him with his brother, they became warriors and Parhelion became a mother and continues to be a protégé to Major. But they start relapsing again because of a bicorn with a split personality named Two-Face Impulse, who sees the both of them as nothing but trouble and after failing to get them dethroned, he aims to get them to become Majes Minor and Mines Major and kill each other through very slick manipulation, revealing dark secrets, and anything it takes, all while pretending through his good personality that he is turning a new leaf, which thanks to his split personality, he actually believes he is, while his evil personality is getting revenge. But Two-Face would not enjoy his unfolded plan for long when he becomes the first victim of his own wicked plan and both sides turn into seperate unicorns, causing the light side and the dark side to end up fighting eachother as both sides are suck into the pools. Now the heroes have to undo a mental-case's stupid mistake and stop a cliamity in the making.