Riinu is a Japanese singer, voice actor, and live streamer, born in Tokyo on May 24, 1998. He is a member of the J-pop group Strawberry Prince. His career in entertainment began in late 2015 when he started uploading song covers to the video sharing site Nico Nico Douga, and he joined Strawberry Prince in mid-2016. As a voice actor, he is sometimes credited under the name Koinu.

Riinu's decision to pursue voice acting was influenced by a childhood friend whose dream was to become a voice actor, and who passed away from cancer during their junior high school years. His early voice acting work includes the role of a young Haruki Serizawa in the 2017 anime Our love has always been 10 centimeters apart, for which he was credited as Koinu. In 2018, he voiced Shiori Gushiken in the television drama Hashiri Tsuzukete Yokattatte. From 2018 to 2021, he provided the voice for the character Shunta Moegi in the long-running anime series Kiratto Pri Chan.

A significant role in Riinu's career came in 2020 when he was cast as Chiaki Hebiyama, and his transformed hero persona Sky Snaker, in the series Yo-kai Gakuen Y: N to no Sōgū, part of the larger Yo-kai Watch franchise. He also performed theme songs for the series. This role extended into related media, including the 2020 video games Yo-kai Watch Jam: Yo-kai Academy Y – Waiwai Gakuen Seikatsu and Yo-kai Sangokushi: Kunitori Wars, as well as the mobile game Yo-kai Watch: Wibble Wobble.

In 2023, Riinu voiced the character Reno Akai in the anime Cardfight!! Vanguard will+Dress. He also had a guest role as a Lie Detector in an episode of The 100 Girlfriends Who Really, Really, Really, Really, Really Love You.

Beyond these roles, Riinu has engaged in recurring collaborations, notably with the multimedia project HoneyWorks. From 2018 to 2019, he was part of the fictional idol unit Dolce within the HoneyWorks universe, voicing the character Fūma Shirayuki. He later reprised the voice role for Fūma Shirayuki in the 2020 video game HoneyWorks Premium Live.

Alongside his voice acting, Riinu has achieved notable success as a recording artist. His debut solo album, Time Capsule, released in December 2019, reached second place on the Oricon weekly albums chart and received a Gold certification from the Recording Industry Association of Japan. His second solo album, Shutter Chance!, released in January 2022, also achieved second place on the Oricon weekly chart and a Gold certification.