Approximal Guide summary:

"...If he doesn't receive guiding, that child will die."The war hero and S-class guide Kang Hajung, whose body is covered in scars. His plans for his long-awaited retirement go down the drain, and to make matters worse, he becomes the guide of the much younger Kim Muhyeok. One day, while on a mission, he is killed by an unidentified esper. As he laments not retiring before his death, he wakes up to find himself in the body of a complete stranger, and even more surprisingly, in the body of a D-rank guide who shares his name"Now that it's come to this, I'm going to retire before anyone finds out."+