Hisayo Mochizuki is a Japanese voice actress and singer born on April 27, 1978, in Tokyo, Japan. She is affiliated with the talent agency 81 Produce. Mochizuki is known for her distinctive, high-pitched voice, which has led her to be frequently cast in roles for young girls and characters with a cute or energetic demeanor.

Mochizuki began her career in the early 2000s. One of her first major television animation roles was in 2000 as Durian in the series Daa! Daa! Daa! (also known as UFO Baby) and as Tattoo in Baby Felix. Her career became closely associated with a number of iconic roles in the early to mid-2000s. She gained widespread recognition for her portrayal of the gentle and soft-spoken Kaho in the 2001 series Sister Princess, a role that would become one of her signature performances. The same year, she voiced the titular character Taruto in Magical Meow Meow Taruto. Following Sister Princess, she voiced Bu-Ling Huang, also known as Mew Pudding, in the 2002 magical girl series Tokyo Mew Mew.

Her career continued with several prominent and long-running roles. She voiced the energetic and diminutive character Yachiru Kusajishi in the immensely popular anime Bleach, a role she played from 2004 through to the series' conclusion in the 2020s, including the final arc, Bleach: Thousand-Year Blood War. She also played the dual roles of Moro and Tattoo in the xxxHOLiC series. One of her most prolific roles was that of Valkyrie (often affectionately called "Waru" by fans) in the UFO Ultramaiden Valkyrie franchise, appearing in the original television series and all its subsequent specials and OVAs, including UFO Ultramaiden Valkyrie 2: December Nocturne, UFO Ultramaiden Valkyrie 3: Bride of Celestial Souls' Day, and UFO Ultramaiden Valkyrie 4: Banquet of Time, Dreams, and Galaxies. Her filmography also includes the role of Tamala in the experimental film Tamala 2010: A Punk Cat in Space, Nana Kimishima in the Pia Carrot e Youkoso!! - Sayaka no Koi Monogatari, Koto Tateshina in the Guardian Hearts OVA series, and Tarurotte in Shattered Angels. In 2008, she also took on a live-action role in the film xxxHOLiC: Rō Adayume.

Beyond voice acting, Mochizuki was also active in music and radio. In 2001, she became a member of the J-pop voice actor unit Prits, formed with her Sister Princess co-stars Nana Mizuki, Natsuko Sugawa, and Yumiko Kobayashi. The group released several singles and an album. She also hosted numerous radio programs throughout the 2000s, often related to the anime series in which she starred, such as Sister Princess and UFO Ultramaiden Valkyrie. She continues to be active in the industry, reprising familiar roles in new projects, such as voicing the mother of her original character Bu-Ling in the 2023 reboot Tokyo Mew Mew New.