Alex

Never seen in the anime, but Rem mentions him. Alex was a friend of Rem's that supported her through troubled times, and it's implied they may have been lovers. His death caused Rem to join Project Seeds as a way to start over. Rem also asks for him to give her strength when she sacrifices herself to save all the other humans on the Seeds ships.

Trivia

 * When Rem cuts Vash's hair, she says his new spiky hairstyle reminds her of Alex, so it's implied he had spiky hair.