Elijah could be on their side. He is Klaus' brother and might understand the importance of the baby, especially if he sees it as a way to keep Klaus in line or to bring about a new era of peace among the different supernatural species. He could use his diplomatic skills to protect the baby from threats.
Some of Bonnie's witch friends might also be allies. They could see the baby as a new source of power or as a being that could change the future of witchcraft. They would offer their magical expertise to keep the baby safe from those who might want to harm it.
The fairies from Sleeping Beauty could potentially be allies. Despite their past differences with Maleficent, they might see the baby as an innocent and be willing to help protect it from greater evils. They could teach the baby about kindness and how to use magic for good.
The main characters are Bonnie, a witch with great power and a kind heart deep down. Klaus, an Original vampire who is both feared and respected in the supernatural world. Their baby is also a main character, which is the focus of the fanfiction. There might also be other supporting characters like Damon and Stefan from the Vampire Diaries universe who could interact with Bonnie and Klaus regarding the baby. They might be curious, or they might be worried about the implications of this new addition to the supernatural world.
For allies, All Might could be an interesting choice even when they are babies. All Might might sense Izuku's potential and also see that Shigaraki could be redeemed if guided right. Another potential ally could be Aizawa. He could be the one who trains them in basic self - defense skills when they are kids. As for enemies, the League of Villains could be a problem for Izuku, as they might see him as a threat to their plans with Shigaraki. Also, some of the more evil - minded heroes who don't believe in second chances for villains like Shigaraki could be enemies.
The other vampire factions could be antagonists. They might see Klaus and Caroline's baby as a threat to their power or way of life. For instance, if the baby has some extraordinary powers, they could fear that it would disrupt the balance of power among vampires. So, they might try to stop the baby from being born or even try to take control of it once it's born.
Allies could include the remaining Stark family members. They would surely support the baby as it is part Stark through Jon. The Unsullied might also be allies as they were loyal to Daenerys. As for enemies, Cersei's remaining supporters could be a threat, seeing the baby as a rival to any power they might still hold. Also, the Night King's followers (if any still exist) could see the baby as a new target, a symbol of the new life they oppose.
You can try searching on fanfiction websites like Archive of Our Own (AO3). It has a large collection of fanfictions from various fandoms, including ones related to Klaus and Bonnie. Just type in 'Klaus and Bonnie baby' in the search bar, and it should show you relevant stories.
One great Klaus and Bonnie baby fanfiction could be about how they deal with the challenges of raising a baby in a world full of supernatural threats. Maybe they have to protect the baby from other vampires or witches who might see the child as a threat or a valuable asset.
One interesting plot could be the baby having special powers due to its unique heritage. Since Bonnie is a powerful witch and Klaus is an Original vampire, their child might inherit a blend of magic and vampire abilities, like being able to use magic to enhance vampire speed or strength. Another plot could be the challenges they face in protecting the baby from the enemies they've made over the years. Enemies might see the baby as a threat or a valuable asset.
Maybe Damon could save her. He's always been protective of those he cares about and he's not afraid to take on Klaus.
Maybe some unexpected allies could emerge. For instance, other dark mages who oppose Zeref's actions for their own reasons. They might see Natsu as a valuable asset or simply dislike Zeref's overbearing ways. Another potential ally could be a powerful spirit that Natsu has befriended in the past. Spirits often have unique powers that could be useful in the fight against Zeref.