Character development is a big part. The characters have to change their initial negative views of each other. In a good 'enemies to lovers' BL novel, you'll see how they gradually start to understand and care for one another. For instance, they might discover shared traumas or interests that bridge the gap between them.
You could also check out 'Given'. Ritsuka and Mafuyu have some initial friction. Ritsuka is a bit cold towards Mafuyu at the start. But through their shared love for music, they grow closer and develop a deep, loving relationship.
Character growth is a key characteristic. The characters start off with negative views of each other. But as the story progresses, they learn to see past their differences. In 'Red, White & Royal Blue', the two main characters grow from being political rivals to lovers, and in the process, they become more understanding and empathetic.
One great 'enemies to lovers' fantasy novel is 'A Court of Thorns and Roses' by Sarah J. Maas. It has a great build - up of the relationship between Feyre and Rhysand. Another is 'The Cruel Prince' by Holly Black. The dynamic between Jude and Cardan is full of tension and eventual love. Also, 'Shadow and Bone' by Leigh Bardugo has some elements of this trope as well.
A good example is 'Wuthering Heights' by Emily Bronte. Heathcliff and Catherine have a complex relationship that starts with a sort of enmity. Heathcliff is treated as an outsider by Catherine's family, and their different social standings create tension. However, they share a deep, passionate connection that evolves into a tortured love. Also, 'Red, White & Royal Blue' by Casey McQuiston features Alex and Henry who are from different worlds (America and Britain) and initially have a sort of rivalrous relationship which then blossoms into a beautiful romance.
First, there's the obvious initial hostility between the main characters. This creates a lot of tension that drives the plot forward. Second, the build - up of sexual tension is a key part, which is what makes it'steamy'. Third, there's usually a moment of realization or a change in circumstances that makes them see each other in a new light and start to fall in love.
Often, these novels also deal with themes of acceptance, not just of their relationship but also of themselves. Since they start as enemies, they have to overcome their own prejudices. In a gay romance context, this can also be related to coming out and dealing with society's views, which adds depth to the story.
The slow - burn aspect is also important. These novels often take time to develop the relationship. The characters go from hating or disliking each other to gradually having feelings. It's not an instant love. In 'The Duke and I', Daphne and Simon's relationship evolves over time as they interact more and more, and their initial animosity fades away bit by bit.
In enemies to lovers romance novels, the characters often have very different personalities or goals that create the enmity. For instance, in 'A Court of Mist and Fury', the main characters are from different worlds with different agendas. There's also the element of forced proximity in many of these novels. This forces the characters to interact more and break down their barriers. Also, the journey of the relationship is filled with self - discovery. As they fall in love, they also learn more about themselves, like in 'You Deserve Each Other' where the couple re - evaluates themselves during the process of falling back in love.
One great example is 'Attachments' by Rainbow Rowell. It has an online aspect where the main characters start as sort of enemies in a work - related online environment. Lincoln, the IT guy, has to monitor the employees' emails for inappropriate use. Beth and Jennifer are two employees who often send emails that Lincoln reads. At first, he seems like an enemy invading their privacy, but as he gets to know them through their emails, he falls in love with Beth. It's a really sweet story that shows how an online connection can transform from something negative to a romantic relationship.
Some excellent 'enemies to lovers' fictions are 'Cruel Prince' by Holly Black. Jude and Cardan are enemies in the faerie world. Jude is a mortal living among the faeries and Cardan is a cruel prince who bullies her. But over time, their relationship changes into something more passionate. 'The Cruel Prince' shows how power dynamics and initial hatred can transform into love. Also, in 'The Vampire Diaries' book series (although it has a TV adaptation too), Elena and Damon start off as enemies. Damon is a vampire who seems menacing to Elena at first, but as the story unfolds, they develop a deep and complex relationship that has elements of love despite their initial enmity.