After the That Time I Got Reincarnated As A Slime franchise previously confirmed that it would begin airing its second season in October as part of the Fall 2020 anime season, news has been released which confirms that the highly-anticipated second season has been pushed to January (Winter 2021). As one can expect, the culprit behind the delay is the COVID-19 coronavirus pandemic, which has been wreaking havoc on anime schedules. Japan recently lifted its state of emergency earlier this week so expect a number of high profile titles to be shifted/delayed as studios begin to adjust their schedule and determine how new social-distancing practices will affect production times.
The anime has also confirmed that it will actually be a split cour, with the first cour (12-13 episodes) airing in January 2021 and the second cour (another 12-13 episodes) premiering in July 2021.
In March 2019, the 25th and final episode of the two-cour first season first confirmed that a second season was on the way. A two-episode OAD (original anime DVD) continuation featuring an original story was released in December. A third OAD was bundled with the manga's 14th volume on March 27. Two more OADs are slated to be released with the manga's 15th (July 9), and 16th (November 9) volume.
That Time I Got Reincarnated As A Slime started out as a light novel series written by Fuse, and illustrated by Mitz Vah in 2013 (it's ongoing and has released 15 volumes to date). A manga adaptation (which is ongoing and currently at 14 volumes), written by Fuse and illustrated by Shō Okagiri is published in Kodnasha's Monthly Shōnen Sirius manga magazine.