Kouji Nayuru

A mental battle against the strongest evil spirit just five seconds after being born... and while he was doing that, his magic power ended up getting maxed out!? Shirakami Kai was reincarnated into an alternate Japan where monsters known as "Spirit Fiends" exist. But when he was born, for some reason, he was caught up in a ritual to summon the strongest evil spirit. A curse tried to kill his mother, after which the evil spirit went on a rampage, trying to take over Kai's body. And while he continued to battle against the strongest evil spirit inside his head, he became an incredibly powerful entity without even realizing it!? Link: Original Web Novel - Kakuyomu

Fifty years have passed since dungeons first appeared on Earth. Dungeon exploration and live streaming are considered the norm for the people. Kuga, who became a dungeon explorer alongside his close friends, ends up being banished from his party due to him being a supposed "jack of all trades, master of none" hero. Amidst his despair, Kuga finds himself thrown into the hidden boss room, famous for making explorers unable to step foot into a dungeon ever again. There, he encounters a beautiful female vampire named Alicia. Though he’s prepared to meet his end, Alicia, captivated by the so-called streaming, has other plans and asks him, "Could you teach me how to stream?" With nowhere else to go, Kuga reluctantly accepts her proposal and thus begins their unprecedented dungeon explorer-hunting streams. For some reason, their stream quickly went viral like crazy, and Kuga then began to awaken some unknown powers...? And meanwhile, something strange is happening to the party members who banished Kuga...