Diana Garnet is an American-born voice actor and J-pop singer based in Tokyo, Japan. Born in Washington, D.C., she was influenced by her father's interest in anime and manga and grew up immersed in Japanese culture, particularly the music used in anime, which motivated her to pursue a singing career in Japan. Her interest was further sparked by two year-long exchanges in Japan during high school and university. Upon graduating from The Evergreen State College, she relocated to Tokyo, initially working as an Assistant Language Teacher while doing freelance narration and vocals for radio and advertisements. She began uploading covers of anime, J-pop, and Vocaloid songs to YouTube and Niconico under the alias Tonkhai, gaining popularity and eventually winning the Spring 2013 edition of NTV's singing competition Nodojiman The World. Following her victory, she signed with Sony Music Artists and made her major debut in October 2013 with the single Mata Kimi ni Koishiteru. Her first original single, Spinning World, was used as an ending theme song for the anime Naruto: Shippuden in 2015, becoming a beloved track among her fans.

As a voice actor, Garnet is known for her bilingual work in English and Japanese across anime, video games, and educational media. In 2017, she provided the English voice for the dual roles of Joule and Lumen in the original video animation Azure Striker Gunvolt: The Anime, a side-story to the video game series. She reprised the role of Lumen for the video game Azure Striker Gunvolt 3. Her other notable English voice roles include Neneko Kosugi in Gal Guardians: Demon Purge, Ayako Katagiri, Jehuty, and Princess Tomato Bomber in Super Bomberman R, and Elise in Little Goody Two Shoes. She voiced Maria Renard in both her youth and adult versions for the game Castlevania: Grimoire of Souls. In 2024, she voiced Alice Thymefield and Sweety in the game Zenless Zone Zero. Garnet has also contributed voice work to fan animations for the game Genshin Impact, voicing Dehya in Nameless Road (2022) and Klee in Progenitor: The Shogunate (2023).

Beyond acting, Garnet has worked as a casting director and voice director on several video game projects, including Gunvolt Chronicles: Luminous Avenger iX 2 and Azure Striker Gunvolt 3. She has also been a co-host for the long-running NHK educational radio program Kiso Eigo 1 since 2018. In 2023, she rebranded her virtual presence under the name Lumin, a VTuber persona through which she releases digital singles and anime theme songs.