Aika Kiryū is a recurring character in High School DxD New, where she is introduced as a second-year student at Kuoh Academy and a classmate of the protagonist, Issei Hyoudou. Her most defining physical traits are her orange hair, which she typically wears in two long braids, and her distinctive glasses. Her appearance is often described as resembling a serious or studious girl, similar to a class representative, which contrasts with her actual personality. Despite this conventional look, she remains fundamentally an ordinary human student in a world filled with supernatural beings.

Aika possesses a personality that is notably frank, open, and eccentric. She is characterized by her warm and friendly demeanor, approaching nearly everyone without prejudice. This includes Issei and his friends, Matsuda and Motohama, who are known throughout the school as a perverted trio and are often shunned by other female students. Unlike most of her peers, Aika does not judge them and maintains a neutral, amicable stance, serving as a rare and valuable source of support within their circle. She is comfortable discussing explicit or mature topics and is known for her sharp, witty, and often teasing remarks. This humor is almost always wielded with underlying goodwill, and she frequently uses it to create embarrassing or comical situations for Issei in particular. Her unshockable nature and lack of taboo make her a unique figure within the school.

Aika’s primary motivation stems from her loyalty and desire to support her friends. She acts as a well-meaning, if unconventional, confidante and advisor. Upon the transfer of Asia Argento into their class, Aika quickly befriends her, becoming one of her closest allies. She takes it upon herself to guide Asia, especially concerning her relationship with Issei, offering advice that is often bold, suggestive, and intended to push the more innocent Asia toward taking romantic initiative. Her role in the story is largely that of a grounded, human friend and a source of comic relief. Even after she inadvertently discovers the supernatural secrets of Issei and his associates in the Occult Research Club, her attitude does not change. She remains supportive, hiding her perceptiveness and care behind her acerbic wit.

Regarding key relationships, her most significant bond is with Asia Argento, whom she supports and counsels. She also maintains a close, teasing friendship with Issei, often at his expense. Her acceptance of Matsuda and Motohama makes her a rare point of contact between them and the other female characters. A notable and unique ability possessed by Aika involves her glasses, which can quantify male virility. This power allows her to make precise and embarrassing assessments of the boys around her, earning her the nickname of an expert in the field. Initially a normal human with no supernatural powers, Aika undergoes a significant development later in the story. In the final arcs, she chooses to join a magician organization to better help her friends, becoming an apprentice to the magician Lavinia and learning the fundamentals of magic and divination.