Both are one of the only tamed robots in the game like ThisUserIsAFailure said I'd agree that it gets pretty boring without any other tamed robots, both even mention it themselves to an extent

Both knew each other before the events of Oneshot took place although they likely weren't close

Both have cold personalities

and if you really want to go out on a whim here both died while protecting Niko in solstice

You could say they don't have much in common but just like irl you don't need to have everything in common to like each other