How Not to Summon a Demon Lord

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 premiered on July 5, 2018.

Plot
From Wikipedia:
 * Takuma Sakamoto is a hikikomori gamer who is mysteriously transported to the 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 passive "Magic Reflection" ability, the spell rebounds, and both end up with magic collars stuck on their necks, thus becoming his slaves 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.

Official

 * Official light novel website (Japanese)
 * Official manga website (Japanese)
 * Official anime website (Japanese)

Other Sources

 * (Light novel)
 * (Manga)
 * (Anime)