The official Twitter account of the Slime Taoshite 300-nen, Shiranai Uchi ni Level Max ni Nattemashita (I've Been Killing Slimes for 300 Years and Maxed Out My Level) television anime announced six supporting cast members on Thursday. The new characters will appear in the anime series beginning episode six (preview below), scheduled to air on Saturday.
Morita began writing the novel on the Shousetsuka ni Narou website in June 2016. SB Creative began publishing the series through its GA Novel imprint the following January, featuring illustrations by Benio. The 16th volume shipped on April 14. The light novel has a cumulative 2 million copies of its volumes in circulation.