Each character fans have thus far met has a unique personality and set of skills that make them a formidable force in future events. Some, such as Daemon Targaryen, promise violence, while others, such as Alicent Hightower, forbode deceit and tragedy. The twelve zodiac signs similarly have diverse personalities, and the characters correspond to at least one of these constellations.
Spoilers for House of the Dragon (show and books) lie ahead!
Aemma Targaryen was Rhaenyra's mother. Everyone loved her, and she was a gentle soul until her untimely death during childbirth. She cared for her family deeply and understood how people worked and felt.
Pisces is a mutable water sign, meaning they go with the flow and are well-versed in reading emotions. Neptune, which rules Pisces, deals with dreams and prophecies. While married to Aemma, Viserys had his prophetic visions. Furthermore, Pisces governed the twelfth house of mysteries and the unseen, and there seems to be something mysterious about Aemma and her death.