Spoiler Warning: The following contains spoilers for Superman #16 by Brian Michael Bendis, David Lafuente, & Paul Mounts.
The Super-Sons was the nickname for the team-up and friendship that developed between Jon Kent (the son of Superman and Lois Lane) and Damian Wayne (the son of Batman and Talia al Ghul). Their friendship took a bit of a stall, however, when Jon accompanied his grandfather into space and aged multiple years in the time it took him to get back to Earth.
While their brief reunion in Superman #16 is sweet, it also reveals one of the most potent tools that Batman has just in case he ever needs to bring down Jon's father.
Robin and Superboy Reunite
Shortly before leaving for the 31st century, Jon Kent decides there's one more person he needs to visit: his best friend, Damian Wayne. Finding Damian embroiled battling Leviathan forces, Jon surprises the newest Robin by having aged so significantly while in space. Damian, furious that his best friend has not only gotten so much taller than him but gone through puberty as well, initially believes it's a trick or a trap.
While trying to figure out what happened, Damian suggests that Jon may have been exposed to Gold Kryptonite. Jon initially seems confused by the concept of Gold Kryptonite, before Damian off-handedly reveals that not only does it exist, but that Batman may or may not have samples of it hidden in a secret vault within the deepest parts of the Bat-Cave... along with all the other forms of kryptonite. Damian specifically says they're for "just in case."
Batman Secretly Stores Kryptonite
Gold Kryptonite is one of the rarest forms of kryptonite. It's also potentially one of the most dangerous. First introduced in the Pre-Crisis DC Universe and periodically appearing over the years, Gold Kryptonite has the power to remove Kryptonians' power completely, more or less reducing them to the strength and durability of an average human. Superman famously used the Gold Kryptonite on himself in Alan Moore and Curt Swan's Whatever Happened To The Man Of Tomorrow as penance for breaking his code against killing to stop a deranged Mr. Mxyzptlk, and would later use it to strip a version of Zod from a pocket dimension of his powers.
The fact that Batman has some on hand isn't surprising. The Dark Knight is typically prepared for any eventually or threat, and that includes dealing with Superman. He even sometimes keeps green kryptonite in his utility belt, again... just in case. But having a sample of the very rare gold kryptonite means Batman has the potential to bring down Superman once and for all, albeit non-fatally. But the question remains: Superman is aware of some of Batman's stores of kryptonite -- in fact, he's given him samples in stories past -- but does the Man of Steel know that at any point, Batman could strip away his powers and end Superman forever?