Fantasy: Kill Immortals with a Pistol in a Low-Martial World

The mercenary traveled through the fantasy world of low martial arts, killed the immortal with one shot without saying a word, and obtained the god-level bone-cutting and marrow-cleansing pill. After swallowing it, his martial arts qualifications became the best in the star field. In order to avoid being killed by immortals in a sneak attack, he determined to practice martial arts to make his body stronger so that he would not be killed instantly. If he was not killed instantly, he would have a chance to draw a gun and kill him. While practicing, if you encounter someone you can't beat, shoot him once. If it doesn't work, shoot him again.