As twin sisters, Maril and Merrill are identical to each other. Both possess the characteristic blue eyes and green-streaked blonde hair of the Cavendish. They are distinguished by their clothes, using the opposite color combination in their dresses and scarves; with Maril wearing a purple scarf and blue or yellow clothing, while Merrill wears a blue or yellow scarf with purple clothing. For their similar hairstyles, Maril's hair is parted to the right while Merrill's is to the left.
As members of the distinguished Cavendish family, both have a polite attitude toward the high-ranking, while showing contempt for the lower class. They both share their mother's visions of letting go of the Cavendish traditions to focus on money.
Maril and Merrill were born in the House of Cavendish, on the secondary side of the family. During their childhood, both mocked Diana for her admiration for Shiny Chariot.
Maril and Merrill appear next to their mother receiving Paul and Andrew Hanbridge in the Cavendish Manor. When seeing Akko with them and then discovering that she does not come from a family of witches, the two make fun of her. During dinner, they present to the Hanbridge family relics who intend to sell them and then witness Diana's declaration of becoming the new head of the House of Cavendish during the Venusian eclipse that very night.
While Daryl stops Diana from arriving at the sanctuary to perform the ritual to inherit the leadership of the family, she orders Maril and Merrill to remain in their room. Even so, they decide to leave, talking about the situation, then receiving their mother after the success of their plan. Akko and Andrew listen to everything, which leads them to save Diana. When Akko and Diana went to the sanctuary, they next to their mother try to stop them, only to fall victim to the curse that protects the ritual, slowly being turned into trees. Diana finally decides to save them, at the cost of losing the opportunity to perform the ritual. Both Maril and Meril gain respect for Diana afterwards, apologizing her for how they were with her in the past.
Maril and Merrill are seen next to the rest of the House of Cavendish, giving their Fuel Spirit to Akko and Diana during their battle against the missile.
Maril and Merrill have great respect and admiration for their mother. She always sees them close to her and supports her no matter what.
Maril and Merrill have a bad relationship with their cousin. Both reject that Diana is the heiress of the family, although they recognize their ability with the magic.
Abilities and Equipment
As Cavendish witches, both Maril and Meril are capable magic users, although they admit to not be as skillful as Diana. Like their mother, they are able to conjure energy snakes through their wands.
- Both "Maril" and "Merrill" are variants of Meryl (Irish, Gaelic) "shining sea".
- The meaning of the name "Cavendish" is "Cafna's pasture", derived from the Old English pre 7th Century personal name "Cafna", itself from "Caf", meaning "bold, daring", plus "edisc", meaning "enclosure or pasture".
- Both sisters and their mother have names ended with リル (riru) in Japanese.
- Their relationship to Daryl is similar to that of Diana's and Hannah and Barbara.