REOL began as a musical unit that consisted of vocalist れをる (Reol), musical arranger GigaP and movie director/producer Okiku. Prior to the group's official formation, both singer Reol and arranger GigaP had worked consistently together, releasing an album, No Title-. The group signed to Toy's Factory in 2015, using the name REOL for the project, and released their debut studio album as a group, Σ, on October 19, 2016.

On August 1st, 2017, REOL announced that they would split, calling it a "developmental breakup". On October 11th, they released their last work as a group, Endless EP. REOL performed together as a group for the last time and disbanded on October 22nd, 2017.

On January 9th, 2018, having teased an announcement four days prior, singer Reol announced that she would continue under the group's name REOL as a solo singer-songwriter signed to the CONNECTONE label, also announcing a mini-album entitled Kyokōshū for release in March 2018. The same day, she publicly released a track from the album, Heimenkyō, that she said would indicate REOL's future direction. Heimenkyō was arranged by GigaP. Read more on Last.fm. User-contributed text is available under the Creative Commons By-SA License; additional terms may apply.