Polaris Solo is a project by Polaris Entertainment that began in January 2018.
In late 2017, they announced, "Next year, we are planning to create an artist who can follow in the footsteps of Kim Bumsoo. [...] We will launch the ‘Polaris Solo Project’ to showcase talented solo artists.”
The first part of the project was Han Heejun's single DEEP INSIDE, featuring Sojung. It was released on January 4th, 2018.
The second part was Sojung's second solo single, Stay Here, released on March 8th, 2018. For the concept, Sojung was described as the "Goddess of Spring".
The third part was Ashley's debut single as a solo artist. HERE WE ARE was released on July 17th, 2018. For the concept, Ashley was described as a "Summer Queen".
It is rumored that Zuny will have a solo comeback in the fall, to go with Sojung and Ashley's spring and summer concepts, but it hasn't been confirmed.