The TV anime “That Time I Got Reincarnated as a Slime” by Yasuki Kawakami and Fuse has decided to produce a 3rd season. The staff unveiled a key visual:

This was announced at the completion screening of “Theatrical Version That Time I Got Reincarnated as a Slime: Guren no Kizuna Arc” held on November 9th at Marunouchi Piccadilly in Tokyo, with Miho Okasaki, Riko Fukumoto, and Megumi Toyoguchi on stage.
Lonely thirty-seven-year-old Mikami Satoru is stuck in a dead-end job, unhappy with his mundane life, but after dying at the hands of a robber, he awakens to a fresh start in a fantasy realm…as a slime monster. As he acclimates to his goopy new existence, his exploits with the other monsters set off a chain of events that will change his new world forever.
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Along with the information on the production decision for the third season, a teaser visual depicting Hinata Sakaguchi confronting Rimuru has also been lifted. We will report on today’s event later.
“That Time I Got Reincarnated as a Slime” is a fantasy story that begins with a salaryman, Satoru Mikami, who was stabbed to death by a passerby and reincarnated as a slime in another world.
The first season of the TV anime will be broadcast in 2018, and the second season will be broadcast in 2021. On November 25, “Theater Version That Time I Got Reincarnated as a Slime Guren no Kizuna” will be released. Both Funimation and Crunchyroll streamed the second part. Funimation also streamed an English dub. Check out best isekai anime.
Source – Tensura Twitter account via Comic Natalie