A good fanfic in this regard would have well - developed characters. The author should stay true to the essence of Clary and Jace as they are in the original work. Their personalities, quirks, and insecurities should be on full display.
Clary and Jace's love is a complex and passionate one. They meet in a world filled with shadowhunters and demons. Their initial attraction is immediate, drawn to each other's strength and beauty. However, they face many obstacles. There are secrets about their families and their own identities that keep getting in the way. But through all the trials, their love endures as they fight side by side against the forces of evil.
You can try Archive of Our Own (AO3). It has a large collection of fanfictions related to Jace and Clary's love. There are various tags you can use to narrow down your search, like 'Jace x Clary' or 'Jace Herondale/Clary Fray' to find exactly what you're looking for.
One popular one could be 'Jace and Clary's Unending Love' where they face various challenges together in the Shadowhunter world and their love deepens through it. Another might be 'Love Beyond the Runes' which focuses on their love defying the rules of the Clave.
Their relationship would become more centered around the baby. They would have to make decisions together for the sake of their child, which would strengthen their bond.
The relationship would evolve significantly. Before the baby, they were mainly focused on their own adventures and relationship. But now, they are parents. They would need to support each other in different ways. For instance, Jace might be more protective of Clary and the baby. Clary would be more nurturing, and they would both have to learn to balance their duties as Shadowhunters with their new family life.
It would change in many ways. They would go from being carefree high school sweethearts to having a lot of responsibilities. There would be more arguments as the stress of the situation builds up. But at the same time, they would also have deeper moments of love and understanding as they face this huge life change together. Jace might become more overprotective of Clary, and Clary would need Jace's support both emotionally and physically.
It depends on the fan base. Some fans are interested in more mature and complex storylines that might fall under Rated R, such as those involving intense emotional turmoil or more graphic action scenes. However, others may prefer more family - friendly or PG - 13 level fanfiction.
I'm not entirely sure if there is a specific 'Jace Superstar Clary Pregnant Fanfiction'. However, considering how creative fans can be, it wouldn't be a surprise. Some fans like to explore different life situations for their favorite characters. You could also check out Tumblr, as sometimes people share links to interesting fanfictions there.
These fanfictions usually build on the existing relationship dynamics from the original source material. They might expand on the challenges that Jace and Clary face as a couple, like dealing with the secrets in their world or the opposition from other characters. And the 'lemon' parts are written to add a bit of spice and heat to their relationship portrayal.