apocalyptic fiction

After the protagonist becomes a zombie hunter, his first weapon is the Desert Eagle. He has a talent skill called Eagle Eye, which can automatically upgrade. Others, such as strength, need Holy Milk to upgrade. After one year, the seal will be lifted. The level will be divided into the type of A, B, C, D, F. Please tell me which novel it is from. Before he became the messenger of zombies, the protagonist met a zombie on his way home. A beauty from school saved him and killed the zombie. However, he was careless and the zombie did not die. In order to protect the beauty, the protagonist was infected. Then the beauty used the Holy Grail to save him. The protagonist became the messenger of zombies. His first weapon was a pistol. The Desert Eagle 70,000 Holy Milk was sucked dry. The Holy Grail of the beauty was broken. The Holy Milk was turbid and she was facing the infection. Then, the beauty did not want to drag the protagonist down, so she knew that her family was behind the protagonist. She went to a place that looked like a zombie hunting ground and opened the door. It seemed that she needed 20,000 Holy Milk.