Koinu is the professional alias for the Japanese voice actor, singer, and live streamer Rinu. Born in Tokyo on May 24, 1998, his career began in late 2015 when he started uploading song covers to the video-sharing website Nico Nico Douga. His talent led to him being recruited in mid-2016 to join the popular J-pop group Strawberry Prince, with whom he continues to perform. As a voice actor, he is most frequently credited under the name Koinu.

Koinu's early voice acting roles include a minor part as a child version of the character Haruki Serizawa in the 2017 anime Our love has always been 10 centimeters apart. His first major role came in 2018 when he was cast as Shiori Gushikata in the original short-form anime series I'm glad I could keep running (also known as Hashiri Tsuzukete Yokattatte), which aired from October 2018. The series, which depicted students striving to become professional voice actors, provided a fitting debut for the up-and-coming talent. From 2018 to 2021, he also voiced the character Shunta Moegi in the long-running series Kiratto Pri Chan.

In addition to his work in anime, Koinu has been active in video games and other media franchises. He voiced the characters Chiaki Hebiyama and Sky Snaker in the Yo-kai Watch franchise, appearing in multiple titles including the anime Yo-kai Watch Jam – Yo-kai Academy Y: Close Encounters of the N Kind and its associated video games beginning in 2020. Between 2018 and 2019, he was a member of the fictional idol unit Dolce, a project by the creative group HoneyWorks, where he voiced the character Fūma Shirayuki. He later reprised this role for the 2020 mobile game HoneyWorks Premium Live. A more recent anime role includes Reno Akai in the 2023 series Cardfight!! Vanguard will+Dress.

Koinu's career is marked by significant achievements in the music industry, which run parallel to his voice acting work. His solo music career, released under the name Rinu, has been highly successful. His debut solo album, Time Capsule, released in December 2019, reached number two on the Oricon weekly albums chart. His second solo album, Shutter Chance!, followed in January 2022 and also peaked at number two on the same chart. He has also frequently collaborated with other artists under the unit name Anipani.