As the six Toa 'Masters' continue to fend off the Skull Army while finding the mask maker, Ekimu and the Mask of Creation, Ekimu forewarned them of the Skull Army discovered an ancient mask, buried into another temple underground, that he sealed away thousand years ago, capable of the user(s) jumping into dimensions, the Mask of Parallel Universe. With that, the Toa rushed towards the temple only for the Skull Army outnumbered them and use the sacred mask to leap into another world. Then they discovered that Ekimu hidden six powerful crystal masks, in par with the Golden Masks, into six sacred shrines from another world as only the Toa and six figures known as the 'Harmonics' can use them to defend off the darkness growing in Okoto. With that, the Toa leap into the wormhole of another world and set out to find the six crystal masks and the 'Harmonics' before the Skull Army does.
In Equestria, 2 weeks after the Battle of the Bands, Twilight and her friends able to live peacefully until a abnormal magical surge happening in the Friendship Rainbow Kingdom and the Tree of Harmony as they discover in the Everfree Forest, 5 skull creatures taking the Elements of Harmony as they set off to fight them only to be outnumbered until six figures arrive to save them. Then as the fight rages on, the Tree of Harmony transformed the Elements into six crystal masks as they scattered across Equestria.
Now both the Toa 'Masters' and the Mane 6 'Harmonics' like the legend foretold, join forces into recover the 'Crystal Masks' before the Skull Army does, but when an old villain now set free once more, they soon discovered that only unity and friendship can overcome the darkest hours.