The Otherworldly Swordsman of Demon Slayer

On a rare day off, the protagonist, an overworked wage slave, heads to Cloudtop Town with his best buddy. He spots a young woman slipping off a little bridge and being swept away by the river in an instant. In a desperate bid to save her, he and his friend jump into the icy water without hesitation. After an enormous struggle, they manage to push her to the bank. But by then, both are utterly exhausted and can no longer climb onto the rocks along the shore. The river sweeps them under. When the protagonist wakes up again, he discovers he's in the world of Demon Slayer. He can't help wondering what kind of people and events he'll encounter in this world. (A fantasy journal from an incurable otaku!)