Shiro Moriya resumed their Soloist in a Cage manga on April 12, 2021 with the 11th chapter, two years after putting the manga on hiatus in March 2019. The manga will continue to update weekly every Monday. As of this writing, the English version of the 11th chapter is not yet out on Shueisha’s MANGA Plus site.
The story of the manga is described as:
This is a prison where every single prisoner is housed, an inescapable cage, which has grown to the size of being considered a “city.” Born and raised in that bleak and snowy city, a young girl lives alone with her baby brother. What will be their fate? Their story of hope and struggle begins here.
Soloist in a Cage launched on Shueisha’s Shonen Jump+ website in September 2018, but went on hiatus in March 2019 due to Moriya’s sudden illness. The English version of the manga launched alongside Shueisha’s MANGA Plus English manga website in January 2019.