Mercelída Ygvar (メルチェリーダ・ユグヴァール), affectionaly called Mer (Mer-san, メルさん) or Merce (Merce-san, メルチェさん) in the anime and Merci in scanlations, is the ruling queen of Ygvar. Her royal name is Mercelída Ygvar I.
Mercelída is the mother of both Rotte and Asuha. When she was 18 years old, after her sisters killed each other for the throne, she ran away from her home and fell into the world tree, where she met Naoya. She conceived Asuha accidentally: she was stranded on Miðgarðr and had to use her Succubus abilities with Naoya despite him being only 12 years old. Even with this brief encounter, she became somehow enamored of Naoya, but tries to keep her distance to allow her daughter's relationship with Naoya to flourish.
Mercelida is a young woman with long light blonde hair, green eyes and a curvaceous body. She is normally seen wearing her hair in a ponytail or down. As a succubus, she also sports pointed ears and tail as well.
Mercelída is the youngest daughter of Queen Ísalind. Born into a noble family, she has seen a horrible side of this life when her sisters had started fighting and killed each other for the throne. She ran away, eventually ending up in the human realm. There, she meets Naoya and tells of her troubles. That night, she has sex with him to replenish her strength to return to her home. This action will later make her the mother of Asuha. She then takes the throne and makes a harem of men for her survival. Three years later, she returns to the human realm to give Asuha to her father to protect from the nobles' life she had to endure. She then has another daughter named Astarotte Ygvar with her husband the king.
She seems to truly enjoy her frivolous life style of having coitus. Although feels terrible that she caused her young daughter to have a fear of men, which then caused the rift between the two of them. Mercelída tries to dish all the hard work as much as possible, but knows when she has to act seriously.
Mercelída seems to be in love with Naoya and he may be the only person she has ever held romantic feelings for. The former is proven when she calls him "Darling" whenever she is speaking to him, daydreams of him and thinks about him at work.
Despite leaving her with Naoya, Mercelída still treats Asuha as a daughter, spending time with her when Lotte isn't around.
Due to a past event that scared Rotte, she and Lotte at first have a very rocky relationship. This is only further exaggerated when Mercelida comes to Lotte's parents meeting days too late. However Mercelida and Astarotte are shown to have started repairing their relationship as the story goes on.