Breaking the Chain

Supergirl and Grace are undercover raiding a yacht. They expose super-powered pirates but are shanghaied into the crew. Kara turns down some sashimi-like food that apparently gives power. She finds a mermaid-like creature with hunks of flesh missing, who asks to be killed to make it stop. Kara flashes back to Krypton where her mother asked to be killed, which she did. Grace, busy fighting the pirates, asks Kara to kill the creature. She can't and is stabbed by the lead pirate. Grace kills the creature, ending the pirates' powers. Before they kill Kara, she is rescued by a new hero, Power Boy.