How Not to Summon a Demon Lord, or in Japanese Isekai Mao to Shokan Shojo no Dorei Majutsu is an anime adaptation of the light novel series written by Yukiya Murasaki and illustrated by Takahiro Tsurusaki. There is also a manga adaptation by Naota Fukuda that’s been published since 2015.
How Not to Summon a Demon Lord tells the story of Takuma Sakamoto, a hikikomori gamer who is mysteriously teleported to his favourite MMORPG, Cross Reverie, appearing as his own character avatar in the game, the demon lord Diablo. The two girls that summoned him the cat girl Rem and the elf Shera attempt to use a spell on him to make him their slave but due to the ability of Takuma’s magic ring, the spell bounce and they turn up with salve collars on their necks, becoming his servants instead. Part of the storyline is him travelling with the girls to find a way to get rid of the slave collars around their necks while helping them with the personal issues that made them summoning him in the first place.