The Defenders was the first time Marvel's small screen heroes joined forces to battle a common threat, as Daredevil (Charlie Cox), Jessica Jones (Krysten Ritter), Luke Cage (Mike Colter) and Iron Fist (Finn Jones) took on the Hand. Despite the characters' subsequent seasons building off the aftermath of that adventure, their hasn't been any confirmation about a potential second season. According to the Marvel Television Executive Vice President Jeph Loeb, a second season isn't impossible.
"No, all we’ve ever said is that there are no plans right now [to do more]. It doesn’t mean that it’s off the table," said Loeb to Entertainment Weekly. "And it doesn’t mean that it even has to be with the original characters that were in the first Defenders."
Loeb went on to expand on his statement that the next potential iteration of The Defenders might not be the Defenders viewers of the Netflix miniseries are familiar with.
"There are lots of Avengers, and through that, you should be able to ascertain that there may be lots of Defenders," Loeb continued. "No one at any time referred to them as 'The Defenders' -- they didn’t wear a little 'D' on their belts, and they didn’t go to a building that had a big 'Defenders' [sign] in the air. They were four mismatched heroes who were joined by a lot of the other heroes that are in the stories that we do on Netflix, but that was that particular story."
So it seems that while Marvel currently has no plans for a second season of The Defenders, they aren't ruling anything out, and if a second season happens, more heroes may join the ragtag team of crime-fighters for a new adventure. But for now, the individual Defenders have their respective missions to keep the streets of New York City safe in their solo shows.