One way to develop their relationship is by showing Robin growing up. Batman can be there for all the important moments in Robin's life, like his first big victory or his first failure. They can also have disagreements and then make up, learning more about each other in the process. For instance, if Robin wants to use a different fighting style and Batman is initially against it but then comes to understand Robin's perspective. This would deepen their father - son connection. Additionally, they could have a shared near - death experience that makes them realize how much they mean to each other.
Their relationship can be developed by having them face challenges together. For example, when they fight a powerful new villain. They have to rely on each other's skills. Another way is through heart - to - heart conversations. Batman can open up to Robin about his past and his fears, making their bond stronger.
In a fanfic, their relationship could be developed by introducing a third character who challenges their bond. Maybe a new hero who tries to replace Robin or a villain who tries to turn them against each other. By overcoming these external threats, they would grow closer. Also, they could have some downtime activities together, like working on the Batmobile or just having a meal together. These simple moments can also be used to show the warmth and love in their father - son relationship.