They would become even closer. The shared responsibility of having a baby would strengthen their bond. Eddie would be more protective of Venom, and Venom would be more gentle towards Eddie, knowing they are in this together for the sake of their future child.
One common theme is the struggle for control. Eddie has to constantly battle with the Venom symbiote to be in charge. Another theme is redemption. Eddie often starts off as a bit of an outcast or anti - hero and through his experiences with Venom, he tries to find a way to be a better person. And the theme of the symbiotic relationship itself is also very common, exploring how Eddie and Venom depend on each other.
One great Eddie Brock Venom fanfiction is 'Venom's Redemption'. It delves deep into Eddie's struggle to control the symbiote and use its power for good. Another interesting one is 'Bond of Venom and Brock' which focuses on the unique relationship between Eddie and the symbiote, showing how they grow and change together. And 'Venom in the City' is also a good read, where Eddie and Venom fight crime in a more urban and gritty setting.
Some fanfictions might take a comical approach. Picture Eddie and Venom trying to live a normal life in the city, but Venom's lack of understanding of human customs leads to all sorts of hilarious situations. Eddie has to constantly explain things to Venom, like why you can't just eat people's pets or why it's not okay to jump from building to building in broad daylight.
One possible plot could be that they face a lot of challenges in preparing for the baby. Maybe they have to find a way to keep the baby safe from Venom's enemies. They might also struggle with how to raise a half - human, half - symbiote child, like figuring out what kind of diet the baby would need.
One possible scenario is that Spider - Man, now as Venom, has to face new and different villains. His powers have changed, so the way he battles foes would be different too. He might have an advantage against some villains who were previously difficult to defeat, but at the same time, he could also attract the attention of more powerful enemies who see the Venom - powered Spider - Man as a greater threat.
Well, perhaps in the fanfiction, Spider - Man is tricked into becoming Venom. A villain could manipulate the situation so that the Venom symbiote attaches to Spider - Man. As Venom, he starts to see the world from a different perspective. His relationships with his friends and family become strained as they don't recognize the changed Spider - Man. He has to find a way to break free from the symbiote's control while still using its power for good.
You can try Archive of Our Own (AO3). It has a large collection of fanfictions, and you can easily search for Eddie Brock x Venom ones. Just use the search bar and type in the relevant tags.
His appearance would change drastically. As Venom, he would be taller, more muscular, and have a menacing look. His costume would be black with the big white spider logo. Also, his relationships would be affected. His friends might be scared of him, and he might have to prove that he is still the same person inside, despite the exterior and some personality changes.