"A Sign of Affection" centers on Yuki Itose, a college student who is deaf and communicates primarily through sign language, written notes, and text messages. Her life takes a turn when she meets Itsuomi Nagi, a multilingual and adventurous classmate who shows a genuine interest in understanding her world. Itsuomi, who has traveled extensively and is fluent in multiple languages, becomes fascinated by Yuki's perspective and begins learning sign language to communicate with her more effectively. Their relationship develops gradually, marked by mutual respect and curiosity, as Itsuomi navigates the nuances of Yuki's experiences and Yuki opens up to the possibilities of connection beyond her usual boundaries.

The narrative explores themes of communication, vulnerability, and the challenges of building relationships across differences. Yuki's deafness is portrayed as an integral part of her identity, shaping her interactions and worldview, while Itsuomi's openness and adaptability highlight the importance of effort and empathy in bridging gaps. Supporting characters, such as Yuki's childhood friend Rin and Itsuomi's friend Oushi, add depth to the story, providing contrasting perspectives on love, friendship, and personal growth. The series balances moments of quiet introspection with tender, heartfelt interactions, creating a story that emphasizes the beauty of understanding and the power of human connection.