Princess Nuala was Abe Sapien's love interest in Hellboy II: The Golden Army.
Nuala is the twin sister of Prince Nuada. When the realm of magical creatures was threatened by humanity, a golden army was created. After much slaughter, the elf king agreed to a truce with the humans. The crown that controlled the golden army was split into three pieces: one for the humans, one for Nuala and one for the king. Nuada would go into exile.
Centuries later, Prince Nuada approached Nuala and their father in an attempt to revive the golden army and destroy the humans once and for all. Nuada had obtained one piece of the crown and gained the other by killing his father. Nuala fled, taking the last piece with her.
Nuala ran into Abe Sapien, who like her had empathic powers. Abe developed strong feelings for her and offered her refuge within the BPRD. Nuala warned Abe that her empathic powers allowed her twin brother to read her mind, meaning he would know where they are. Nuada found them, kidnapped Nuala and mortally wounded Hellboy. Abe, Hellboy, Krauss and Liz travelled to Ireland to confront Nuada. Abe provided Nuada with the last piece of the golden crown in exchange for Nuala's safety. Nuada summons the golden army and would have killed them, but Hellboy challenges Nuada for the right to command the army. Hellboy wins, but Nuada tried to stab him when his back was turned. Nuala managed to stop her brother by stabbing herself, the damage being transferred directly to Nuada. Both died, but not before Abe let Nuala know his feelings for her.