Luckily, Mr. Kim's temper was much better than they had imagined.

Seeing that Kim Haru didn't press the matter further, they slowly stood up.

Kim Haru had originally only asked about their injuries to change the subject, but now he had heard a term that piqued his interest.

"Energy crystals?"

From his experience playing so many games, Kim Haru knew that something like "energy crystals" would definitely be important in an apocalyptic setting. He still remembered that after killing twenty zombies earlier, he had collected ten of these crystals, though he didn't know how to use them.

Maybe his farming system needed energy crystals too. Otherwise, why would the system have required him to kill enough zombies to activate it in the first place?

As expected, though Shin Woncheon didn't understand why Mr. Kim would ask about energy crystals, he didn't dare speculate on his intentions. Instead, he thoroughly explained everything he knew about their uses.

Just as Kim Haru had guessed, energy crystals played an enormous role in the post-apocalyptic world.

As with the settings in many apocalyptic novels, the energy crystals formed in the brains of zombies were filled with the energy that ability users needed. The higher the level of the zombie, the more energy the crystal contained, and the darker the color it appeared.

Besides providing energy to ability users, energy crystals had become the hard currency of the apocalypse. Over time, they had replaced money, becoming the most coveted "currency" for everyone.

In addition to energy crystals being a form of currency, there was another widely accepted "currency" in the various safety zones: points.

"Originally, each safety zone had its own point system, but a few years ago, as people began to move more frequently between the zones, the leaders of the safety zones unified the point system, making it universally accepted," Shin Woncheon explained as he showed the back of his hand to Kim Haru.

People like Shin Woncheon, who frequently went out to battle, often had their belongings stolen, lost, or discarded in haste. Initially, points were stored on cards that resembled pre-apocalyptic bank cards, but these were too easily lost. Eventually, they switched to nanotech chips, which were implanted directly under the skin.

Most people chose to have their chips implanted on the back of their hand, as it was convenient for scanning and posed no health risks. Now, on the backs of Shin Woncheon and his team's hands, there was no trace of the implants.

Kim Haru quietly took note of all this information.

Shin Woncheon and the others then took out their energy crystals to show Kim Haru, explaining the basic differences between them.

Zombies, like ability users, had different elemental attributes, and the energy crystals from them had distinct characteristics. In fact, they were quite easy to differentiate. For example, Shin Woncheon's metal-type energy crystal was represented by a small metallic orb at the center of the crystal. The whole thing looked like an intricate decorative item.