Trinity in Tempest

That Time I Got Reincarnated as a Slime: Trinity in Tempest (転生したらスライムだった件 異聞 ～魔国暮らしのトリニティ～) is a spin-off manga illustrated by Tae Tono. It was first published on magazine's "Suiyōbi no Sirius." The manga centers on Phos, a girl from the Beast Kingdom of Eurazania. Phos, Stella, and Nemu go to Tempest on secret orders from the Demon Lords. On March 18, 2020, Kodansha announced its license to the manga. They will release the first volume in English on October 20, 2020.

Synopsis
The new spinoff manga to the hit fantasy isekai series, developed by original creator Fuse! Against the odds, the little slime Rimuru has established his magical kingdom for all monsters, called Tempest, and it’s thriving. But three visitors, Phos the fox girl, Stella the dragon girl, and Nemu the winged girl, come to pay Tempest a visit, they’re stunned at just how quickly it’s developed. Don’t miss this new story in the world of Slime, just as the second season of the anime arrives!