Magister Negi Magi. Uncharacteristically suggestive comments and thoughts from a character usually considered pure and innocent. Sometimes this is played straight and shows that a character is mature or smart enough to notice subtle themes their friends don't. Most of the time it's a trait given to a shy character to show they're not quite as mousy and meek as we think.
Usually cued by fantasy segues becoming more and more lewd. This will always be fiercely denied by the character, especially if they're cantankerous and dismissive.
The more comedic princess-like types often get this too until it turns into a more overt Running Gag. Note that the title refers to covertness in the figurative sense, not the literal. This trope is also Truth in Television β you know who you are. Don't say it; otherwise, you won't be one anymore. For example, she was the only one of the then six girlfriends to object to trying to peep on Rentarou in the bath. Nevertheless she is shown to occasionally have more adult-oriented thoughts, especially if the circumstances suit her tastes.
For example, when Nano is dressed up as a prince, Shizuka's love of Fairytale Motifs causes her to start taking photos while drooling, a response usually reserved for Lovable Sex Maniac Hahari. When all the girls are taking turns giving Rentarou a Lap Pillow , Rentarou has dreams related to the girl he's resting on; his dream with Shizuka is becoming intimate on their honeymoon night and Rentarou's response to immediately wake up and sit bolt upright. He later responds the exact same way to the actively sexy dreams given by Hakari and, again, Hahari.
Shino Aizawa of Aizawa-san Multiplies dreams of being rather intimate with her crush, Souta, but she's generally too shy to admit it. However, she develops a Literal Split Personality sprung from her carnal desires, who is most pointedly not afraid to admit it, and the original as well as duplicates based on other aspects of her personality doesn't exactly deny what her libido is saying.
