The Hades we see in the future is the product of the goddess mind raping him to that point. Basically the Hades when Jill is 16 has been driven insane by the goddess's plot as the story unfolds. For some short details, Hades loses everyone close to him, stuff like making him having to execute a "brother" was very close to him as a person, burning down cities, etc.
As for the goddess's plan, she's in love with Rave, and Hades, being the physical reincarnation of Rave is the target of her obsession. Her plans are to ruin and destroy EVERYTHING in Hades' life so that the only thing that remains is her. The thing is that the goddess can possess ANYONE over age 14. Hades' mother is implied to have been possess and killed herself to further break Hades. Sofia in the original timeline was also possess and went on the murder spree for that reason as well. This is why Hades was so hell bent on a girl being under 14, he was worried that before he could make her the dragon princess that the goddess would nom nom nom that girl to inflict more pain upon Hades. For those people still thinking that Hades is a pedo, he's actually not, he's so pure that he doesn't even know where children come from so he doesn't really understand that his remarks can be... Misinterpreted.
The WN so far has completed 2 arcs. And thanks to Jill being a badass, she has broken 2 very major plots against Hades by the goddess already and managed to protect his happiness. In the first arc, (manga is currently on this one), she managed to prevent Sofia from being killed, stop an entire family from being executed on Hades' orders, and protects the city. As a bonus, the goddess makes as appearance as a spear (Rave takes the form of a sword) to which Jill snaps in half. And then throws the shattered remains back to Kratos (The WN translator uses Kratos so I think I'll use it here too) all to the laughing tune of Rave.
In the 2nd arc, Jill prevents Hades from having to execute his brother and settle things with his family, namely to prevent him from falling, she promises 10 children. Yes, she promises to have 10 of his children and tells him that they'll marry them off to his "brother" and "sister" so that they'll be officially part of the real Rave royal family. She calls it their "happy family plan". I want to paint the scene: Hades is looking like his insane self years from now, he's so pissed off that he's releasing a torrent of magic that's blowing everyone away and Jill and clinging to his waist trying not to be blown away. As Hades is ranting about the injustice in his life and wants to make everyone regret being born Jill yells "I'll give birth to 10 of his majesty's children!". Everyone freezes, Hades' magic instantly stops. Jill then adds "I have 7 siblings, and my sister just popped out 3 kids! I come from a very fertile family, I can definitely do it!". It was both funny and heartwarming given what was revealed in the arc.
As a final spoiler, its heavily implied that the goddess is either already in control of the little sister ( the incest prince and princess) or that the little sister is like Hades and is the reincarnation of the goddess Kratos. Arc 2 ends with Jill declaring war on both the princess and the goddess, though privately as princess just started summoning the goddess's powers and Jill was in no shape to fight something like that.