After leaving Mount Ida, Hades decided that it was best that he return to the Underworld, teleporting there immediately.
He appeared in his throne room before his throne and he immediately felt the change in temperaure. It was much colder here than on Mount Ida. It was also less comfortable; where the breeze and scenery on Mount Ida was soothing and calming, the aura of the Underworld was harsh and tyrannical, unwelcoming of outsiders.
'About time I change that.'
Hades was now certain that Zeus wouldn't be on his case should he develop the Underworld more. After all, he had aready given his permission.
His first order of business was to build an ornate golden hearth a few metres away from the base of the stairs. On that hearth, one could see depictions of the Totanomachy and how the Olympian Gods came to rule 'The Universe'.
This was done for 2 reasons. Firstly, it allowed for some more warmth in his throne room. Yes, as Lord of the Underworld, he should be a terrifying figure, but Hades wanted to at least be comfortable when seated on his throne.
The second reason his vow to his new mother. In hindsight, he had bitten off more than he could chew, namely in his promise to mend his relationship with his siblings. Especially Zeus. That man may as well have a sign saying 'STAY AWAY FROM ME OR SUFFER' that would light up around his siblings.
Hades hoped that by having a hearth in the Underworld, Hestia would be able to come visit. He knew from canon that Hestia became the Goddess of all hearts after Prometheus stole some of the coals from hers on Olympus and gave them to humanity, prompting them to make hearts of their own. Going by that logic, Hestia must have a connection to ALL hearths, even if she has yet to become the goddess of them. (A/N: At this point, Hestia is only Goddess of The Hearth I.e: the one on Olympus)
Lo and behold, Hestia appeared soon after the hearth was completed. She had a look of confusion on her face.
"Hades? You built a hearth?" she asked. Then realisation dawned on her face. "You built a hearth! Now I can come to visit!"
She rushed up and jumped into his arms for a hug. Seeing this, he stood up and descended the steps, meeting her halfway.
"Thankyouthankyouthankyouthankyou," she gushed into his chest. "I can finally visit you outside Olympus! I tried to get Poseidon to put a hearth in his castle, but he just shrugged me off! 'Why would I need one' he says! Oh, thank you, Hades! You have no idea what this means to me!"
Apparently, Hestia had been trying to get him and Poseidon to put hearths in their palaces so that she could come and visit them more easily. Poseidon didn't really care about that, which hurt Hestia's feelings.
Also, it appeared that she had been wanting to ask him too, but because he hadn't gone to Olympus for 200 years prior to the last Winter Solstice, she had been unable to ask. And when she did want to, he got caught up in discussion with Zeus.
'Really, it made sense why she wants to visit, family bonds and all that. But from a purely pragmatic viewpoint, I can see why Poseidon refused.'
Since it appears that Hestia's divine authority was linked to all hearths and not just the one on Olympus, she should be able to teleport to any hearth, as she had just done. Poseidon may be unnerved by that, not to mention how, if he is to maintain his sense of authority and dominance in the oceans, Hestia would need permission before entering his watery halls. A hearth in Atlantis does away with all of that, allowing her free access whenever she wished.
Given how they had just overthrown their father, who had overthrown his father before him, I can see why Poseidon would be sceptical of family. Not to mention how he had a thing against Zeus, feeling that he would make a better king of the Gods.
But having read the Percy Jackson books, Heroes of Olympus and regular Greek mythology, he knew that Hestia was the least threatening Olympian diety due to her love for her family, going so far as to willingly cee her throne on Olympus to Dionysus to prevent war amongst the Gods.
Not to mention how cute and bubbly she was when she got like this. He could almost imagine her as the cute loli sister in a slice of life anime that has the protagonist wrapped around her pinkie by virtue of her cuteness and innocent appearance.
Feeling strong compulsions from his inner brotherly spirit, he gently patted her head, getting a satisfied hum in return.
"Thank you for trusting me like this," Hestia said, looking up at Hades.
'Ah, so she DOES understand what having unrestricted access could possibly mean.
"Of course, Hestia," Hades replied. "You're my most lovable sister. How could I not? That would be a crime!"
She seemed to protest at that.
"Oh, my dearest princess Hestia. Please bestow your most gracious forgiveness on this humble servant of yours," Hades said, followed by a mock bow.
She giggled and nodded in mock approval, trying her hardest to suppress her laughter.
"You are forgiven Hades," she said, pointing her nose to the sky in a pretend snobbish manner. "Now go about the rest of your menial duties."
They both broke out into laughter. Hades decided that now would be a good time to direct them to his personal quarters so that they may sit and talk to each other.
The two of them talked at great length about everything that was going on, Hades being perfectly willing to listen to Hestia's gossip. It seems that on Olympus, she didn't really have anyone to talk to.
Hades, Poseidon, Demeter and most of the Titans were never on Olympus, Zeus was always busy with something, Hera would always butt heads with her and the servants in Olympus treated her too deferentially for them to talk to her normally. In the end, she was very lonely.
They talked for a couple more hours before Hestia felt that she had to return to Olympus. HAdes hugged her before she left, reassuring her that his door was always open to her. She teleported to Olympus with a smile on her face, but not before promising that she would come much more regularly.
Hades was unable to squash the melancholy growing inside. He felt like he was James again spending time with his sister Lily. So closely did Hestia resemble her in character and attitude. He could almost picture her smiling at him, her golden locks shining in the sunlight.
'No. I'm not that man anymore.'
Taking her promise to heart, he decided to furnish an apartment for Hestia to stay in if she decides to stay for longer periods of time. He then decided that it would be prudent to make one for his mother Rhea and another for Hecate in the event they ever decided to come to the Underworld.
He then looked outside and decided that it was time to get to work in full swing.
Now that he had the go-ahead to do as he wished in the Underworld, he began planning to create inhabitants for his realm and create a civilisation to rule over. He had two options: he could either attract other races to the Underworld or he could create his own. He knew that by using a human as the base, he could create an entire species, as Athena had done with Arachne, creating spiders, and Zeus with Lykaon of Arcadia, creating lycanthropes.
As for races that could be attracted to the Underworld, he could maybe look towards the devils of the Ars Goetia, but he wasn't sure how he compared to Lucifer or if the devils would even accept living in his domain.
That would all depend on whether the devils were in conflict with Heaven and the Abrahamic God or if Satan was condemned to suffer in Hell alongside his devil race for their arrogance and want to make sure more humans suffer in Hell with them.
Then there were the demons of China (yaoguai) and Japan (yokai). There were probably others, but these were the more powerful ones that he could think of that he actually may have a chance of recruiting.
Creating his own race would mean he had more control over them and it would be simple to bring them to the Underworld, but it would be in much smaller numbers.
Inviting another race would mean he would increase the population by a large amount and instantly create a city of sorts in his realm with the possibility for growth, but he would have less control over them and it would be harder to get them into the Underworld.
He decided that it would be best to try his hand at both and see where things go from there.