The Ice Walker of the Apocalypse

The end of the world is coming, and zombies are rampant. A man as cold as ice discovered that after killing zombies, he could dig out a crystal from their brains. If he swallowed it, he would gain a memory that was not his own and a short-lived ability. And beside him, there was a woman who was "assigned". The only rule between the two is: don't talk about the past, don't ask about the future, just trade.