Fiona Frost

Fiona Frost (フィオナ・フロスト) is a spy for WISE who acts under the codename "Nightfall" (〈〉). She works undercover as an assistant to Loid Forger at Berlint General Hospital to provide him with mission details.

Appearance
Fiona is a pale woman of average height with bobbed hair of a light lavender color and a long fringe covering much of the right side of her face, worn swept behind her left ear. She has cold purple eyes framed by light-colored eyelashes, and most often is seen wearing an emotionless expression.

Fiona is introduced wearing a large duffel coat with a black turtleneck and pants underneath, and her outfit during her time at the Forgers' house consists of a black blazer and a low-dip light shirt. Her stud earrings take the shape of WISE's symbol.

Personality
After being trained by Loid Forger to hide her true emotions, Fiona tends to remain emotionless on the surface—even when making a mental confession of love to Loid she kept her stone-cold face plastered on. She thinks of herself as the superior partner to Loid and wishes to separate him from Yor Forger so that they can be together.

History
Fiona was trained under Twilight to become a spy who didn't let their emotions get in the way of the mission. However, the more she works alongside Twilight the more she ends up developing feelings for him. When Twilight was assigned Operation Strix, she wished to be working with him as his wife but at the time she was unavailable because she was doing another operation. Instead, she was placed in Berlint General Hospital to work undercover as an assistant to Twilight so she could provide him with information on missions. The more she watches Twilight, the more she realizes he's developing real feelings for the Forger Family but she finds this trait of his even more endearing. When the two of them are assigned to retrieve the painting "The Lady in the Sun" she lists them as husband and wife for the tennis tournament, showing her feelings for him.

Campbelldon Tennis Arc
Fiona is seen talking to Sylvia about Operation Strix. Fiona asks her that if the current wife decides to leave her roll, she would replace him, but Sylvia confused asks her what is she talking about, but after hearing no reply from her she warns Fiona not to plan anything crazy. Fiona arrives at the Forger residence and is welcomed by Yor. Fiona, as a trick to make Yor retreat her roll as a wife, starts talking about how she heard Loid complain about his wife. When she was about to finish, Loid returns home with Anya after taking Bond out for a walk and is surprised to see Fiona, her fellow agent Nightfall, inside talking with Yor. He asks Fiona what she's doing here and Yor tells him that she came to return Anya's magnifying glass which was left behind at the hospital. Loid thinks that something urgent must have happened and explains that they returned early as it looked like it was about to rain. As Loid and Fiona hold a conversation, they mouth different words to communicate secretly. Fiona states that she's here to assess the state of Operation Strix. Fiona asks Loid if walking Bond is an essential part of Operation Strix and why it wasn't Yor doing the errands instead. Seeing his talents being wasted on playing house, she suggests they review his operational tactics but Loid tells her it isn't her place to do so. Anya got aware of her feelings, so she started planning ways of preventing Yor being replaced. While they were talking, Fiona thinks to herself how much he loves Loid and her desire to become his wife.

As it starts to rain, the two agents sit down to continue their conversation and Yor brings Loid his coffee with some milk. As he thanks Yor and takes his drink, he hopes that the milk will lessen the damage to his stomach and considers asking Yor to switch him to decaf. Anya tells Yor her cocoa is the best one, so Fiona tells Anya that she has an imported cocoa in a chance to win her trust, which Anya happily gasps but then tried to stay focused on praising Yor. Anya clings onto Yor and calls her the best mother in the whole world for wiping up her cocoa, since Anya tried to show Fiona she doesn’t need a new mother. A touched Yor tells Loid that she's going to try harder for the family. Loid smiles, and assures Yor that she works hard enough as Anya cares a lot about her, reminding her that she is already a great wife. Fiona recognizes that Loid’s smile was showing emotions, so then she excuses herself and leaves shortly after. Twilight notes that she forgot her umbrella and decides to walk her to the station. Twilight runs after Nightfall, and she tells him that she's been assigned to partner with him on the next mission. Twilight asks how could she forget something so important, and is surprised after she turns to him with a sad expression on her face, as she was crying. Nightfall says that she will contact him with the details at the hospital before walking away, telling Twilight that playing house has made him soft and not to drag him down in their joint mission.

Abilities and Skills
Poker Face: Fiona is able to conceal all of her emotions, making it impossible for anyone to tell what emotion she is feeling. At all times she has a stone-cold look at her face whether she's happy, upset, angry, or even proposing her love.

Physical Strength: Fiona has massive physical strength, shown when she took multiple opponents in tennis, and to some degree even managed to rally a shot by Yor.

Loid Forger
Twilight served as a mentor during her training as a spy, teaching her to bury her emotions and show no weaknesses. Likely because of this time that she spent with him, Fiona fell in love with Twilight and now has a certain ambition to become his wife in place of Yor, who she deems unsuitable for such an important role.

Yor Forger
Fiona thinks Yor is lacking as Loid's wife and is jealous of the fact that a woman far less skilled than her in being a wife gets to be his wife and that Yor can manage to evoke some genuine positive emotion from Loid when in his company.

Anya Forger
Fiona believes that Anya is not raised strictly enough, and under her (very painful) guidance, she can be made into a Stella Star procurement machine.

Chapter Appearances

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Trivia

 * The name Nafalia Foney she made up the tennis tournament is derived from her agent codename "Nightfall" (same for Twilight's alias Twain). In Japanese, she used the name "Tobarī" (トバリー) which is also a derivation of her Japanese codename, "Tobari".
 * The fake last name, Foney, is a humorous nod toward the "phony couple" they were acting as.
 * Nightfall's chair, featured on the cover of the sixth volume, is a Panton Heart Cone.

Quotes

 * (To herself, after seeing Twilight’s serious mode): “There it is. That’s the Twilight who won my heart. The Twilight I can’t stop chasing. The Twilight I want at my side. The Twilight who turned my respect into love. The Twilight whose dreams became my dreams. What I’m saying is… I love you”.
 * (To herself): “What a wonderful man you are Twilight. I’ll achieve peace between East and West. And I’ll do it all for you”.