I've Been Killing Slimes for 300 Years and Maxed Out My Level
I've Been Killing Slimes for 300 Years and Maxed Out My Level is a Japanese light novel series written by Kisetsu Morita and illustrated by Benio. It was serialized online since 2016 on the user-generated novel publishing website Shōsetsuka ni Narō and, in the following year, it was acquired by SB Creative, who published the first light novel volume in 2017. The light novel has been licensed in North America by Yen Press, who published the first volume in April 2018. It has received a manga adaptation in the same year as its debut of the light novel in Square Enix's Gangan Online website. An animetelevision series adaptation has been announced. In September 2019, a spin-off light novel called Hira Yakunin Yatte 1500-nen, Maō no Chikara de Daijin ni Sarechaimashita was launched, while a manga adaptation of the same name was also launched at the same time. At the same month, another spin-off light novel called Reddo Doragon Jogakuin debuted at Gangan Online website and app.
After living a painful life as an office worker, Azusa ended her short life by dying from overworking. So when she found herself reincarnated as an undying, unaging witch in a new world, she vows to spend her days stress-free and as pleasantly as possible. She ekes out a living by hunting down the easiest targets—the slimes! But after centuries of doing this simple job, she's ended up with insane powers...how will she maintain her low key life now?
Originally, the series was published by Kisetsu Morita on the user-generated web novel site Shōsetsuka ni Narō in 2016. The publisher SB Creative acquired the series and then began publishing it on their GA Novel imprint as a light novel in January 2017. Ten volumes have been released as of August 2019. Between January and July 2018, in the volumes 5 to 7 of the light novel, a special story about the character Beelzebub was published at the end of those volumes. In September 2019, those stories were compiled into its own volume and the spin-off called Hira Yakunin Yatte 1500-nen, Maō no Chikara de Daijin ni Sarechaimashita was published on September 13, 2019 by SB Creative on the GA Novel imprint with Kisetsu Morita and Benio as the author and illustrator, respectively. In September 2019, another spin-off light novel called Redo Doragon Jogakuin with Kisetsu Morita and Benio debuted at Square Enix's website and smartphone app Gangan Online with the first chapter released on it but still without a tankobon release for the novel.
In June 2017, Square Enix began publishing a manga adaptation of the series by Yusuke Shiba in their online website and smartphone app Gangan Online, with five tankōbon volumes released as of September 2019. A manga adaptation of the spin-off light novel Hira Yakunin Yatte 1500-nen, Maō no Chikara de Daijin ni Sarechaimashita was launched on Square Enix's Gangan Online website and smartphone app, with Yusuke Shiba reprising his work.
An anime television series adaptation was announced during a livestream for the "GA Fes 2019" event on October 19, 2019.
The light novel ranked ninth in 2019 in Takarajimasha's annual light novel guide bookKono Light Novel ga Sugoi!, in the tankōbon category.