Aimer is a Japanese pop singer and lyricist who emerged as a significant figure in anime music following her 2011 debut. Her stage name is derived from the French verb meaning to love, and for her work as a lyricist, she is often credited under the name aimerrhythm.

Aimer was born on July 9, 1990. Her early exposure to music came from her father, a bassist, and she began playing violin in elementary school. During her junior high years, she was inspired by Avril Lavigne to learn guitar. A pivotal moment in her vocal development occurred at age fifteen when she overused her vocal cords, leading to a period of silence therapy. Upon recovery, she developed the distinctive, husky, and低沉沙哑 vocal quality that defines her recordings.

Her professional career launched with the 2011 single Rokutousei no Yoru, which was used as the ending theme for the anime series No. 6. Her second single, released on December 14, 2011, featured the song Re:pray. This track was selected as the twenty-ninth ending theme for the long-running anime series Bleach, specifically used for episodes 343 through 354. Re:pray was subsequently included on her first studio album, Sleepless Nights, which was released on October 3, 2012.

Aimer has maintained a consistent and high-profile presence in the anime industry. Her notable soundtrack credits include Re: I Am and StarRingChild for Mobile Suit Gundam UC. For the Fate series, she performed Brave Shine as an opening theme for Fate/stay night: Unlimited Blade Works, with Last Stardust appearing as an insert song within the same series, and later contributed I beg you and Haru wa Yuku for the Fate/stay night: Heaven's Feel film trilogy. She provided the ending theme Ref:rain for the series After the Rain, and the song Torches for Vinland Saga. More recently, her work includes Zankyōsanka for Demon Slayer: Kimetsu no Yaiba, Deep down for Chainsaw Man, and escalate as the opening theme for Nier: Automata Ver1.1a.

Her musical identity is characterized by a low, husky vocal tone that conveys both warmth and melancholy. Her style encompasses emotive ballads and more energetic, rock-influenced compositions. She has worked with prominent producers and artists, including composer Hiroyuki Sawano, with whom she has frequently collaborated on projects such as Mobile Suit Gundam UC. Her fourth studio album, Daydream, released in 2016, featured high-profile collaborations with Taka from ONE OK ROCK and Yojiro Noda from RADWIMPS. For much of her early career, she performed without public appearances, maintaining a degree of anonymity until revealing her face on the music program Music Station in 2016.

In the industry, Aimer is regarded for her commercial success and critical recognition. Her 2021 song Zankyōsanka became her first to reach number one on the Japan Hot 100 chart, and she has performed at major venues including the Nippon Budokan. She releases music under the Sacra Music label and is managed by Agehasprings. In 2023, she married musician Masahiro Tobinai.