Star Trek: The Next Generation (1987) : 5x17

Stardate: 45614.6. While investigating the disappearance of a J'naii shuttlecraft, the crew finds reason to believe the missing ship is stranded in an abnormal pocket called "null space." Riker and Soren, a member of the J'naii race, begin preparing to rescue the craft, and the two strike up a friendship. Their relationship develops quickly as the pair question each other about mating habits, since the J'naii are androgynous and do not identify themselves as either male or female. Despite this difference, sparks begin to fly between them.