When Monica left, the people in the base finally came out. As soon as they stepped outside, they were stunned by the sight before them. Goodness! Thirty pieces of alloy steel plates appeared before their eyes, and unaware of the situation, they thought they had entered an underground bunker.

"David, did you do all of this?" Arnold asked incredulously as he tapped on the steel plates. David smiled and nodded, leaving Arnold even more amazed.

"Wow! With this defense in the base, even the Zombie King would cry and leave. David, you're truly awesome!" Arnold exclaimed, giving David a thumbs-up.

Sally and Duke also looked at him in astonishment. They couldn't believe that in just one morning, David had reinforced the defense of the base to such an extent.

You see, each of these alloy steel plates weighs at least a thousand kilograms, and David effortlessly arranged them. The group couldn't help but have a renewed appreciation for David's strength. As they looked at everyone's astonished faces, David smiled faintly. What he had done now was just physical defense for the base. Although it could withstand some low-level and even high-level zombies, it probably wouldn't be very effective against intelligent zombies like the ones with higher intellect.

At the same time, the voice of the system sounded in his ears.

[ Ding!]

[Congratulations, Host, on completing the initial upgrade of the base's physical defense system!]

[Triggered new mission: Upgrade the base to an Apocalypse base!]

[Time: 8 days, 15 hours, 53 minutes]

Upon hearing the system's voice, David frowned slightly. "Upgrade the base to an Apocalypse base?" The system detected David's confusion and spoke again in his ear.

"The Apocalypse base is the most formidable base during the apocalypse, capable of withstanding all apocalyptic calamities, including zombie attacks."

"Survivors in the Apocalypse base can enhance their own supernatural abilities based on the fortress's level of advancement."

"From low to high, the Base can be upgraded to six levels: Black Iron, Bronze, Silver, Gold, Diamond, and King."

historical

As David listened to the system's explanation, he gradually understood. He then asked quietly in his mind, "How can I upgrade the base?"

He knew that upgrading the base would definitely require some resources. If it was only crystals, he had no need to worry because the amount of crystals piled up in his warehouse was astounding. However, he vaguely felt that upgrading the fortress wouldn't be as simple as just crystals. After all, it was a matter concerning the survival of the survivors and their hiding place.

"To upgrade the base to the Black Iron level, 10,000 primary crystals are required."

"To upgrade the base to the Bronze level, 10,000 intermediate crystals are required."

"To upgrade the base to the Silver level, 10,000 advanced crystals are required."

Upon hearing the system's pricing, David couldn't help but twitch at the corner of his mouth. Spending 10,000 primary crystals to upgrade the base to the Black Iron level was acceptable to him, but the Bronze level required intermediate crystals, and the Silver level required advanced crystals...

David couldn't help but think, "Is this an upgrade or a robbery? These are high-level crystals! Even as a resources tycoon like him, the number of advanced crystals in his warehouse was extremely limited. Furthermore, David knew that the higher the base level, the higher the quality of crystals required. Who knows, maybe a King-level base would require all sorts of special crystals."

David thought he could live carefree in this world, with crystals all around him. But after the system's offer, he fell silent because he realized, in an instant, that even if he gave everything he had, he could only upgrade his base to the black iron level.

However, considering the importance of the Doomsday base, David nodded silently. The higher the level of the base, the stronger the support for their team members. They wouldn't even need to consume crystals to upgrade their abilities. When David calculated it, he found it worth it.

So he decided that in the days to come, he would hunt zombies diligently to obtain crystals. There was no other way. The road ahead was long and arduous, and great responsibilities would fall upon them. To ensure the strength of his team, he had to be fully committed.

At this moment, David decided to spend 10,000 junior crystals to upgrade his base to the black iron level. He looked at his base and silently called out to the system.

[Ding!]

[Host's intention to spend 10,000 junior crystals detected. Upgrading the base to the black iron level fortress.]

[Please confirm, host!]

"Confirmed!" David decisively affirmed in his mind.

[Ding!]

[Base is currently upgrading!]

David stood aside, observing the changes in the base. Suddenly, a surge of energy emerged from all around. This energy quickly enveloped the entire base. After a few minutes, the energy dissipated.

[Ding!]

[Congratulations, host. Base upgraded to the black iron base!]

The system prompt of the base being upgraded to a fortress resonated in David's ears, prompting him to eagerly look. In an instant, the ordinary base seemed to have a subtle metallic feel. Not only the walls but even the load-bearing walls emitted a faint metallic glow. However, the appearance of the fortress still appeared to be covered in cement, without any noticeable changes if not observed carefully.

With this upgrade, David successfully transformed his base into a black iron fortress, further improving its defensive capabilities. Seeing the upgrade completed, David smiled. It had to be said that spending those 10,000 junior crystals was worth it. Just these metallic load-bearing walls could withstand many attacks for their team.

Entering the fortress, David noticed that the interior remained mostly unchanged. However, as soon as he stepped inside, an invisible aura instantly infiltrated his body. This aura was as comfortable as the flowing of a spring or a murmuring stream.

Suddenly, under the influence of this aura, David felt a sudden ripple in his heartstrings. "Did I reach level six?" Feeling the ripple in his heart, David was surprised. He didn't expect that a black iron-level Base would grant him such a boost. It instantly elevated him to level six, exciting him. If things continued like this, leveling up their team would be like child's play.

The others also heard David's words and quickly approached, their faces filled with astonishment. "You've become a level six superhuman?" David nodded.

Sally stared at David, her eyes seemingly wanting to dissect him. Arnold, Sophie, and Duke looked at David as if he were a monster.

David smiled faintly and said, "Don't look at me with such strange eyes. I only leveled up by one level." But his words instantly sparked anger. How could you call becoming a level six superhuman "just" leveling up by one level?