Goblin

"Right, with food being so scarce, why not trade it for a magic crystal? Man, I'm such an airhead!" Alex's little noggin lit up with a spark of inspiration.

After all, magic crystals weren't exactly rare commodities, perfect for those Lords running low on grub. But Essence Shards were a different story, only dropping from level 5 and above, a high-tier resource.

Alex figured not many folks had Essence Shards. Those lucky enough to have them probably summoned some powerful troops and wouldn't be short on food either.

[Hamburger initiates a trade!]

[One unit of food for forty units of wood, twenty units of stone, or one magic crystal.]

[Remaining quantity: 1,800 units.]

One unit of food for one magic crystal, sounds fair, right?

Yeah, totally fair.

Alex nodded unconsciously.

Once Alex's offer hit the All-Races Fair Trade, it stirred up quite the commotion again.

[UnpaidBill]: "I'm a girl, I can do anything for you!"

[CaptainPanties]: "Even though I'm a boy, I can do the same..."

[LordOfTheFries]: "Now I'm really curious what Hamburger's troops are. They can't actually be hamburgers, right?"

[Snorezilla]: "Let me guess, Hamburger's Lord must have some massive troops, only big troops could pack such a punch!"

[ToiletPaperThief]: "No kidding, what else could it be if not big troops, mice?"

...

Soon, Alex started receiving system notifications that trades were happening. This time it took nearly ten minutes to complete all trades.

Alex also got a ton of friend requests, too many to count, just showing up as three red dots...

Being an orphan, Alex had come to this world alone, with no friends or family to speak of, so she felt no guilt in hitting 'reject all' with a single click.

...

Alex checked the trading post and ended up with a whopping haul of 30,000 units of wood, 15,000 units of stone, and 300 magic crystals. It was the biggest score ever!

Alex was over the moon. The special structure, the Bone Throne, was still out of reach due to a shortage of Essence Shards. Looks like she'd have to keep hunting high-level creatures tonight. 

But upgrading the castle? She had that in the bag. The warehouse was now stocked with an impressive 34k wood and 17k stone, while the castle upgrade only needed 10k wood and 5k stone. Talk about having room to spare.

Based on previous upgrade requirements, Alex figured she could probably bump the castle up two levels this time around. But she needed to save materials for the Bone Throne, so she decided to upgrade just one level for now.

[Castle Level: lv7]

[Health Points: 50k (Invincible)]

[Territory Area: 5 square miles]

[Feature: Within the territory, the Lord has the right to see everything, along with the ability to Disassemble and recycle from the Warehouse.]

[Special Structure: Maiden's Wardrobe]

[Upgrade Requirements: 12k wood, 6k stone]

Sure enough, there was still enough material left for another upgrade, but Alex wasn't tempted. The easier upgrades often turned out to be less impressive. 

She knew that special structures unlocked at levels 3, 6, and 9, and wondered just how high the castle could go—maybe up to lv100?

"Arthur!"

"From now on, you're mainly in charge of taking down high-level wild creatures for leveling up. Also, scout around for any other local forces. Leave the hunting to the other undead."

Alex instructed Arthur, who bowed in response.

"Yes, my respected Queen."

Then, the remaining 456 undead were split into three groups. Two groups of a hundred undead each took on the tasks of mining stone and chopping wood, led by a few lv3 Phantoms. 

The remaining 200+ undead continued hunting, but those assigned to stone and wood were all lv1, summoned by Alex. This way, the higher-level undead and those with room for advancement could continue hunting to gain experience. 

Alex had maximized this detail to its fullest.

Alex had already noticed that she wasn't the only one selling food on the World Chat channel; many other Lords were peddling grub too. 

While a few Lords had prices matching hers, some had started to slash their rates. However, these were just small deals, and Alex's bulk orders weren't affected yet. 

The food market was cooling off, and although Alex's castle kept leveling up and her territory expanding, it was clear that the local wild creatures were nearly hunted to extinction by her skeleton crew.

The undead labor force was limitless, but the number of wild creatures was not. So, Alex decided to divert some of her undead to chop wood and mine stone, capitalizing on their infinite labor.

"Seriously, even if zombies are dumb as bricks and can't snag kills to level up, they should at least handle some mining and lumberjacking, right?"

Meanwhile, Arthur was soaring above, hunting wild creatures around the castle. As the local beasts became scarce, he used his aerial advantage to venture further from the castle. 

Just then, he spotted a group of green humanoid creatures below—likely a local force. With the advantage of the skies, he dove down, unleashing a breath of dragon breath.

The green creatures couldn't dodge in time and were frozen by the dragon's breath, their souls extinguished. Only one, a mage-like figure wielding a staff, managed to magically dodge to the side and hurled a fireball at Arthur.

Boom!

The smoke cleared, and Arthur was unscathed.

[Passive Skill: Elemental Magic Immunity!]

The green humanoid mage was terrified and tried to flee, but Arthur landed in front of him, roaring mightily. The sheer force of the dragon's roar and its imposing presence caused the mage to kneel, trembling.

"Please... don't kill me!"

Arthur ignored the plea. This intelligent creature surely knew about the local forces around the castle. He grabbed the mage with his claw and took flight.

Back at the castle, Alex suddenly received a series of system notifications.

[Your troops have killed a level 5 Goblin Warrior, gaining thirty experience points.]

[Your troops have killed a level 4 Goblin Warrior, gaining twenty-five experience points.]