The person who requested the designs explained the following:
In their region, there's a species of Gyarados that is actually the original Gyarados. (The one from Kanto is actually a regional form.)
So, Magikarp climbs waterfalls with great determination and evolves into Dorakoi, which then evolves into Gyarados after successfully reaching the top.
In their region, there are also studies indicating the existence of a species from the same evolutionary group, named the Gilded Leviathan, a primitive monster from the distant past.
And finally, there's the concept of Primal Reversion, a special phenomenon unique to this region. Through it, a Pokémon merges with its ancient genetic data (in this case, Gyarados + Gilded Leviathan), resulting in the mighty Primal Gyarados.
by formigaartz