The Demon Lord and the Summoned Hero

Kanda Touya is summoned by a god to another world as the hero, and tasked with the quest of defeating the demon lord Rava.

Note: Despite being labeled as an Isekai wa Smartphone to Tomo ni. doujinshi by the scanlator, this manga is in fact an original work, as stated by the artist himself. The main character in Isekai Smartphone is named Mochizuki (望月) Touya, not Kanda (神田) Touya, and there is no Demon Lord Rava in it.