#but genuinely their relationship is so fascinating in robin war. like having duke and damian paralleled so closely is SOOOO interesting

[casscainmainly]

As much as I love Duke and Damian being the most adorable brothers ever, the tension between them is way underutilised. They both have very tenuous relationships to the Robin identity, and if you look at their interactions in Robin War, it's shot through with insecurity and dislike:

Specifically, Damian consistently refutes Duke's right to Robin. Robin War is the event that leads Duke to quitting Robin, and arguably he does this mostly because of Damian; Tim and Jason don't really interact with Duke, and Dick essentially endorses him. But the beef is not one-sided, because Duke consistently hits on Damian's insecurities as well:

Damian belittles Duke's friends and entire cause; Duke highlights how unwanted and abandoned Damian is. They are simultaneous Robins with incompatible views of what Robin should be. Damian, fresh from his journey in Robin: Son of Batman, sees Robin as atonement, a link to Batman, and a representation of his personal growth; Duke, in the middle of We Are Robin, sees Robin as power, freedom from adult authority, and a representation of collective community.

The worst thing Damian can say about Duke is that his Robin is meaningless; the worst thing Duke can say about Damian is that his Robin is alone. They both say that to each other. And then, they both give up Robin:

In Duke's case, he precedes saying "I'm not Robin" with "that's the difference between you and me." Their Robins are so wildly different, their ideals so opposed to each other, that they cannot co-exist as Robin. The risk of losing what Robin means to them, especially for Damian, fuels a lot of their early animosity.

This opposition continues in Batman & The Signal #1, where in Duke's dream sequence, there is only one person he imagines wanting to oust him from the family - Damian. But Bruce also pits Damian and Duke against each other in Batman: The Secret Files: The Signal, in Duke's favour:

Bruce drags Damian down ('requires continuous supervision') to uplift Duke ('Gotham's best'). The writing in this comic is very questionable, but this is reminiscent of the way he talked to Cass about Steph in Batgirl (2000). Cass is the acceptable girl vs. Steph's unacceptable femininity; in a similar vein, Duke is the acceptable Batkid of colour, whereas Damian's heritage is 'inconvenient'.

Which is why it's all the more important that, despite everything, Damian and Duke do love each other.

Damian, despite all his (understandable) ambivalence and outward disdain towards Duke, pretty much spends the entire comic trying to save him:

And Duke, when Damian defects to the Owls, staunchly refuses to believe he's gone for good. Tim and Jason also protest, but they get knocked out pretty quickly. It's Duke who refuses to give up on Damian. It's Duke who won't leave Damian alone.

Even though their Robins are complete opposites, Duke and Damian both know how big a deal it is to choose Robin; as the two Robins of colour (besides Dick, whose position is slightly different), they know how easily Robin can be taken away. It's why Duke, a virtual stranger, is the one to break through to Damian when nobody else could.

This panel from the end of Robin War hits so hard in context. Every interaction up until this point is antagonistic, and they have every reason to hate each other - but they don't. They choose not to. They choose to love each other instead.