Kotori Koiwai is a Japanese voice actress, narrator, lyricist, and composer affiliated with the agency Peerless Gerbera. She was born on February 15, 1990, in Kyoto Prefecture. Her interest in voice acting was sparked during her childhood by the vocal performance of Pikachu in the Pokémon anime. While in high school, she worked as a narrator, an experience that solidified her ambition to pursue a career in voice acting.

Koiwai made her professional debut in 2011 with a minor role as Yoshikuni in the anime Blue Exorcist. Her first major roles came in 2012 and 2013. In 2012, she voiced Kigurumi Haroukitei in Joshiraku. The following year, she landed her first leading role as Iwai Mushanokōji in The Severing Crime Edge and also began voicing one of her most iconic characters, Renge Miyauchi, in the long-running and beloved slice-of-life series Non Non Biyori. This role, which she has reprised across multiple sequels, OVAs, and a feature film, is among her most recognized performances.

Throughout her career, Koiwai has demonstrated considerable versatility, taking on a wide array of characters across different genres. She voices the fairy Elaine in the fantasy epic The Seven Deadly Sins, appearing in several installments including Dragon's Judgement and Imperial Wrath of The Gods. She plays the mysterious Utsutsu Miya in Gatchaman Crowds and the quiet白石 (Shiraishi) in Tanaka-kun is Always Listless. In comedy series, she is known as Mano in Teasing Master Takagi-san and as Kururi Saotome in Val x Love. Her filmography also includes roles such as Saori Rokugou in Pastel Memories, Anzu Takanashi in Real Girl, Kuku in I've Been Killing Slimes for 300 Years and Maxed Out My Level, Ren Shibusawa in After School Dice Club, Yukie Kanoko in Godzilla Singular Point, RiN in Princess Connect! Re:Dive, and Koume in Engimon. She also provided voices for the series Okoshiyasu, Chitose-chan and characters such as Mei Merrihada in Battle Spirits Double Drive, Rinse and Yuni in Chain Chronicle, Nono Ōji in Aikatsu!, and Mebuki Konoe in Magica Wars. Her work extends to video games, where she is known for roles like Millium Orion in The Legend of Heroes: Trails of Cold Steel series, Tomoka Tenkubashi in The Idolmaster Million Live!, and Yun Jin in Genshin Impact.

Beyond voice acting, Koiwai is a multifaceted creative talent. She is an accomplished lyricist and composer, having written music for fellow voice actress Rie Tanaka and for the character song Sister, performed by her character Tomoka Tenkubashi, which marked her major debut as a songwriter. She is proficient in music technology, having passed the MIDI检定 1级 (MIDI certification Level 1). In 2019, she formed the metal band Dual Alter World with a member of the band Blood Stain Child and also began working as a DJ. She has provided the voice bank for the Vocaloid characters MEIKA Hime and MEIKA Mikoto. In 2020, she founded her own ASMR label, kotoneiro, through which she creates and releases immersive audio content. This venture led to a collaboration on the video game Kemono Teatime, an ASMR adventure game released on Steam and Nintendo Switch.

Koiwai's diverse skills and unique personality have brought her recognition within the industry. In 2019, she announced that she had been accepted into Mensa, the international high-IQ society. In 2021, she was awarded the Influencer Award at the 15th Seiyu Awards, which honors voice actors who have gained significant attention beyond standard voice acting work, particularly on social media. Her career continues to thrive with ongoing voice roles in series like SHY and The Most Notorious "Talker" Runs the World's Greatest Clan, as well as the upcoming sports anime Medalist.