How Not to Summon a Demon Lord, also known as The King of Darkness Another World Story: Slave Magic (Japanese: 異世界魔王と召喚少女の奴隷魔術, Hepburn: Isekai Maō to Shōkan Shōjo no Dorei Majutsu, transl. "The Other World Demon Lord and the Summoning Girl's Slave Magic") is a Japanese light novel series written by Yukiya Murasaki and illustrated by Takahiro Tsurusaki. The light novels are published in English by J-Novel Club. A manga adaptation by Naoto Fukuda has been running since 2015, and is licensed by Seven Seas Entertainment. An anime television series adaptation by Ajia-do Animation Works aired from July 5 to September 20, 2018. A second season by Tezuka Productions and Okuruto Noboru aired from April 9 to June 11, 2021.
 Takuma Sakamoto is a hikikomori gamer who is mysteriously transported to the virtual world of his favourite MMORPG, Cross Reverie, with the appearance of his own character in the game, the Demon Lord Diablo. The two young girls who summoned him, the pantherian Rem and the elf Shera, attempt to use a spell to make Takuma their servant, but due to his magic ring with the ability "Magic Reflection", the spell rebounds, and both end up with magic collars stuck on their necks, thus becoming his servants instead. With a serious case of social anxiety, Takuma decides to act like his character while interacting with others, and makes use of his high stats and vast knowledge of Cross Reverie's lore to survive in his new environment, traveling along with Rem and Shera to look for a way to remove their slave collars, while helping them with their own personal issues that led them to summon him in the first place.
 The light novels are written by Yukiya Murasaki and illustrated by Takahiro Tsurusaki. Kodansha published the first volume under their Ranobe Bunko imprint in December 2014. J-Novel Club announced on September 28, 2017, that they had licensed the series for the North American market.
 Naoto Fukuda launched a manga adaptation of the series on Kodansha's Niconico based manga service Suiyōbi no Sirius in June 2015. Seven Seas Entertainment announced their license to the manga on September 14, 2017.
 An anime television series adaptation was announced in January 2018. The series was directed by Yūta Murano and written by Kazuyuki Fudeyasu, with animation by studio Ajia-do Animation Works. Character designs for the series were provided by Shizue Kaneko. Yuki Nishioka was the chief animation director. Yuki Miyamoto provided monster designs and serves as action animation director. Backgrounds were provided by Kusanagi, while Natsuko Otsuka was the color key artist. Photography for the series was directed by Teppei Satō at Asahi Production Shiraishi Studio, and Satoshi Motoyama directed the sound at Half HP Studio. The series aired from July 5 to September 20, 2018, and was broadcast on AT-X, BS Fuji, Tokyo MX, and Sun TV. The series' opening theme, "DeCIDE", was performed by the unit SUMMONERS 2+, a group composed of voice actresses Azumi Waki, Yū Serizawa, Yumi Hara, Rumi Okubo, and Emiri Katō, while the ending theme, "Saiaku na Hi demo Anata ga Suki." (最悪な日でもあなたが好き。, "I Like You Even on the Worst Day."), was performed by Serizawa and produced by HoneyWorks. The first season ran for 12 episodes.
 Crunchyroll simulcast the series worldwide outside of Asia, while Funimation streamed a SimulDub of it in North America. Following Sony's acquisition of Crunchyroll, the English dub was moved to Crunchyroll. In South and Southeast Asia, Medialink licensed the series.
 On April 8, 2020, it was announced that the series would receive a second season titled How Not to Summon a Demon Lord Ω, co-animated by Tezuka Productions and Okuruto Noboru, and directed by Satoshi Kuwabara, with the rest of the staff and cast members reprising their roles. The second season aired on TBS and BS-TBS from April 9 to June 11, 2021.  The second season's opening theme, "EVERYBODY! EVERYBODY!", and ending theme, "YOU YOU YOU," were performed by Serizawa with collaboration by DJ KOO & MOTSU. The second season ran for 10 episodes.
 The How Not to Summon a Demon Lord light novels had over 1 million copies in print as of March 2018. On January 4, 2023, the Australian Classification Board refused classification for How Not to Summon a Demon Lord Ω but did not provide a reason. The decision means that the second season of the anime "cannot be sold, hired, advertised or legally imported in Australia", although it is still available for streaming.