That Time I Got Reincarnated as a Slime is a Japanese fantasy light novel series written by Fuse, and illustrated by Mitz Vah. It was serialized online between 2013 and 2016 on the user-generated novel publishing website Shōsetsuka ni Narō. It was acquired by Micro Magazine, who published the first light novel volume in 2014. Twelve volumes have been released as of July 2018. The light novel has been licensed in North America by Yen Press, who published the first volume in December 2017. It has received a manga adaptation published by Kodansha along a manga spin-off published by Micro Magazine and an anime television series adaptation by 8-Bit.
Fuse originally serialized the series as a web novel on the user-generated content site Shōsetsuka ni Narō between February 20, 2013 and January 1, 2016. The series was acquired for print publication by Micro Magazine, who published the first light novel, with illustrations by Mitz Vah, under their GC Novels in May 2014. English publisher Yen Press announced their license to the series during their panel at Sakura-Con on April 15, 2017.
The light novel series has over 4.5 million volumes in print. The light novel ranked eighth in 2017 in Takarajimasha’s annual light novel guide book Kono Light Novel ga Sugoi!, in the tankōbon category. It ranked sixth in 2018 and fifth in 2019. The light novel series was the 5th best-selling title of 2018 with 539,277 and its manga adaptation was the 9th best-selling title of 2018 with 3,460,066 copies.
The anime adaptation won best anime awards for its protagonist Rimuru Tempest on Crunchyroll anime awards 2019.