How NOT to Summon a Demon Lord: Volume 10 by Yukiya Murasaki

MMORPG Cross Reverie's top player, Takuma Sakamoto, is summoned to another world where he's forced to play the part of his in-game character, Demon Lord Diablo! Diablo has successfully saved Faltra in his greatest battle yet, but there's no rest for the weary!

A summons arrives from the Kingdom of Lyferia, demanding Diablo make an audience with the king. However, Diablo also learns the wedding ring he gave Rem actually forms a pair with Shera's! Diablo teams up with Faltra's guildmaster, Sylvie, to arrange an official substitute.

"Endeavor in my name. I'll allow it!"
"Let's go on an adventure then—to the Viridian Cathedral!"

This is the tenth volume of the adventures of an earth-shakingly powerful Demon Lord (or at least someone who acts like one) taking on another world!