Plot
Supergirl is with the Legion in the 31st century, trying to find a way back to the 21st century. Brainiac 5 is showing her his new invention, a chronexus, which is a time viewer. While tuning it, it picks up alternate versions of Superman from a lateral timeline, but finally picks up on the Superman from Supergirl's era. They witness his birth on Krypton, then the launching of his rocket. It then goes through his years with the Kents, from a baby through 8th grade. It then shows his first public super-feat, rescuing a space plane, and then Dr. Berkowitz' accident that turns her into Blackstar, and Clark's subsequent first "date" with Lois. Then, it shows an early Justice League encounter, Clark and Lois now married talking about children, and Superman fighting various villains. Then, it shows Supergirl's first appearance on Earth, and some of her history there, including Superman's admission to Lois that it's great to have a family again. Supergirl is speechless watching that. Finally, the machine shows another adventure with Blackstar, one that Supergirl doesn't remember, so it occurs in her future. Supergirl wants to help the situation, so she insists that Brainy send her back there, mentally at least as he can't do it physically. He does, and she does help, but by "possessing" Superman, and leaves a message for him from her. But then the machine starts to act up. It shows several events from Supergirl and Superman's future: Superman fighting various Brainiacs (who resemble various past comic, TV, and comic strip incarnations), Supergirl finding her parents alive, then something that could be an enlarged version of Kandor with a woman later revealed to be Karsta Wor-Ul standing there. Finally, the machine finally blows apart, but Supergirl makes it back to the 31st century. Finally, we flash back to the 21st century, and Superman reads the message that was left for him, letting him know to hang in there, that he's not alone.