Splatoon is a massive success and very popular for Nintendo, but while one would think they would be the first ones to make a mobile game for the IP, they were beaten to the punch by China.

The game completely copies assets, music and core mechanics from the Wii U game mostly well on mobile and shows a Splatoon portable game can be possible. Below is a video of the game in action.
https://www.youtube.com/watch?v=IlZQYZGCRAg
More on the story as it develops.
Source: Eurogamer