Rivermouse

An ordinary man from Earth is suddenly transported to Aetheria, a vast fantasy world of magic, monsters, adventurers, demons, elves, Beastkin, spirits and ancient dragons. Civilization once wielded legendary S, SS and EX-tier magic, but a catastrophe called the Great Severance stripped most of the world of magic above B-tier. Now an ancient evil known as the Hollow King stirs beneath forgotten ruins. The newcomer possesses an impossible, unique ability called Eclipse: any magical effect he deliberately invokes through it succeeds with absolute certainty, regardless of resistance or magical tier. Its only true limitation is the enormous mana cost and extreme fatigue it causes. As he learns magic, joins the Adventurer Guild and builds a party, he will uncover the truth behind Eclipse, his summoning, the lost age and the returning evil. Along the way, genuine friendships, romance and multiple Soul Bonds may develop.

You are an ordinary man from modern Earth, abruptly killed in an accident and transported to a world of magic and political intrigue. As compensation, you have been granted an immense reserve of mana and the ability to manipulate it with scientific precision. You awaken in a foreign land, surrounded by unfamiliar customs and dangers, with the weight of a mysterious purpose pressing upon you.