When Supergirl came down to Atlantis, he volunteered to show her around, quickly becoming enamored of her. After she defeated a series of ancient weapons accidentally let loose on Atlantis, Jerro told her she was lovely. During a celebratory pageant held in her honor, Jerro competed in a race. The two prizes for the winner were a trophy and a kiss from Supergirl. Jerro won, and Supergirl kissed him. Supergirl, herself becoming enamored of Jerro, quickly left Atlantis when she realized the Atlanteans were privy to her thoughts during and after the kiss, despite Jerro's asking her to stay longer. ("Supergirl's First Romance!")
He attended her sixteenth birthday party soon after, along with Lori and Ronal. He gave her a giant pearl as a present. ("Supergirl's Busiest Day!")
Jerro began spending more time with Lenora Lemaris, who fell in love with him and shielded her thoughts so he wouldn't find out. The two became close friends.
When Supergirl became Super-Mermaid due to the effects of Red Kryptonite, she visited Jerro again. Jerro, still in love with her, proposed marriage. Supergirl hesitated, because she also had feelings for Dick Malverine. Jerro saw this in her mind, but tried to convince her regardless. However, his affection for her made Lenora despair, and she ran off into the Valley of the Hands. Supergirl and Jerro had to rescue her. Soon after, Supergirl reverted to a normal Kryptonian and returned to the surface. ("The Strange Bodies of Supergirl!")