Plan to read - action

Yeon-woo had a twin brother who disappeared five years ago. One day, a pocket watch left by his brother returned to his possession. Inside, he found a hidden diary in which was recorded "By the time you hear this, I guess I will be already dead."

Like in "No Longer Human" (Ningen Shikkaku) , the protagonist of this story attempts a double suicide with his lover... but gets hit by a truck and summoned to another world instead.