The original black coloured cube, started trembling a little, followed by shaking wildly which gave Natsu a scare thinking that it couldn't bear with the egg's weight.

Luckily, the cube suddenly stopped shaking and almost allowed Natsu to breathe a sigh of relief when pieces of it began falling down.

Seeing this Natsu's mouth fell wide open with fear, but he managed to not scream and began to observe because Rias had told him to place the Fire Dragon Queen's Egg on top of the Dungeon Core, and she would never suggest him anything which could cause him harm.

And indeed, as more and more of the black coloured layer surrounding the cube fell down, a bright red coloured texture began revealing itself from underneath it.

Soon, the original black cube had completely turned red, with bright yellow coloured cracks on it that made the cube seem like the surface of a volcanic cave, with streams of lava flowing through it.

Oddly enough, as Natsu took another step back to observe the cube along with the egg on top of it, he felt that the both of them quite suited each other.

It was around the same moment when Natsu realized this, that he obtained a notification from the DH System.

[The Great Tokyo Dungeon's, Dungeon Core has evolved!]

[Check the Dungeon Core's Status for more details.]

Seeing this, Natsu immediately looked towards the lava cube and willed for its Status to appear.

[Great Tokyo Dungeon's, Dungeon Core (Lvl 1)

DP Produced Per Day - 250

Type - Fire Dragon Core

Benefits - Fire Type monsters deal additional 10% damage, and the recovery rate is increased by 10%

Dungeon Monsters related to Dragons deal additional 10% damage, and the recovery rate is increased by 10%

Dungeon terrain can be changed to a fire based terrain for free

Dungeon Monsters living inside the fire based terrain have a 5% chance of evolving into a fire type monster

Fire type monsters deal addition 10% damage, and the recovery rate is increased by 10% when inside a fire based terrain]

Reading all of this, Natsu's breathing sped up from how many various possibilities it provided for his Dungeon to grow up in.

And the number of benefits it brought to him.

Fire type terrain? That was just a simple way of saying lava filled Dungeon!

Immediately calling for Rias, Natsu began asking the various questions he had regarding the benefits provided by the Fire Dragon Core.

After clarifying all of his doubts Natsu felt both happy and sad.

Happy, because the additional damage dealt and recovery rate would stack up into 30% if a monster was of fire type, related to dragons, and inside a fire based terrain.

And sad, because the 5% chance of evolving into a fire type monster didn't mean that 5 creatures out of 100 had the chance to evolve.

Instead, each beast had a 5% chance to evolve.

Either way, the Grand Lucky Draw had given Natsu not just an egg which had the potential to become a strong living breathing dragon in the future, but also made his Dungeon Core evolve.

In fact, it was due to this that the Great Tokyo Dungeon would soon in the future get a new nickname, the Dungeon of Fiery Death.

But that was all for the future, now that Natsu had learned about all the potential benefits his mood no longer even had a trace of the previous depression and disappointment.

Seeing that Natsu had now completely recovered, Rias said, "With how many points you have darling, you can now choose to remodel the Dungeon like you always wanted to."

Hearing this piece of news, Natsu once again made a note to never let his emotions get the best of him, and opened the DH System to add an additional floor to his Dungeon.

It cost 50,000 DP to add one extra floor to the Dungeon, 5,000 to make a tunnel, 15,000 to create a maze, and so on.

Luckily, when the second floor was created, the Dungeon would create stairs to join them, sparing Natsu from the cost of creating them.

However, if he wanted another to create a second connection between the two floors, he would need to pay for it.

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Going back to the bed and sitting down, since he needed to think properly before making changes to his Dungeon, which couldn't be edited or changed again until he added another floor, Natsu came up with a plan pretty soon enough.

Resting in between Rias's embrace, with Carla on his shoulders, Natsu once again checked if everything was as he wanted and pressed the confirm button.

And in the next second... Nothing happened.

Blinking his eyes in confusion, Natsu looked around to see, but felt that nothing had changed, or was changing.

"It's already done, Master."

"What?"

Unable to understand what had finished, Natsu looked towards the Dungeon map to see that it truly had changed.

His Dungeon now had a second floor, and the ground floor was no longer a tunnel connected to a wide soccer field like space. Instead, it looked like a honeycomb with five tunnels from the entrance running three fourth way through the rectangle Dungeon, and seven more tunnels intersecting the first five which originated at the spot where the stairs to the first floor were at.

On the first floor, Natsu filled three fourth of the floor with a maze, and left the final one-fourth space to be empty.

That place would be where Natsu would live, along with Rias, Erza, Carla, and the Dwarfs. Due to this, Natsu split the final empty space into two halves. One for him, and the other one for the Dwarfs to work.

Also, Natsu turned the entire Dungeons terrain into a molten lava one, other than the part he would be living at.

As for the reason Natsu wasn't able to see any of the changes that happened, it was because the Dungeon changed in an instant, and there were many furniture around him, which blocked his line of sight.