 How Not to Summon a Demon Lord

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.