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.

Personality
After being trained by Loid Forger to hide her true emotions, she has remained expressionless. Even when making a confession of love to Loid she had a 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.

Emotionless
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, angry, or even proposing her love.