

Īlthough majority of the tracks were commissioned throughout its production process, Reol stated that the song "Re:" was originally left out of the final product. Similarly, the group told that songs like "Give Me a Break Stop Now" delves into Reol's anger and irresponsibility, while "YoiYoi Kokon" was inspired by the Gion Matsuri event in Kyoto, and represents a sign of celebration and change. In an interview with Billboard Japan, the members commented that the lyrical content emphasizes enjoyment and how they are feeling at current state, noting it as "transitory" they had chosen the album tracks "YoiYoi Kokon" and "Give Me a Break Stop Now" as examples of this. This allowed the singer to compose the tracks herself, resulting into the three album inclusions "VIP Kid", "Re:" and "404 Not Found". However, Reol started to re-edit the track and after completing it, she Skyped GigaP the results. The first song created for the project was "Detarame Kidding", an "interesting" collaboration between the two but was briefly shelved. According to GigaP, the record was heavily influenced by Westernized music, both contemporary pop and EDM, and also noted inspiration of K-Pop and modern Korean pop culture. Despite the groups experimentation with J-Pop, general pop music and indie rock music, both as a trio and individually, Sigma is an electronic dance album that incorporates elements of hip-hop and club sounds. Additionally, Hiromichi Takiguchi mastered the record alongside GigaP, which was finalized on September 1 with the music videos. The album was recorded between 20 in Japan, and was mixed GigaP. The material on Sigma were written, composed and produced by member Reol, whom also provided vocals to each track bandmate, GigaP, received additional music credits towards composing and arranging the album. But on August 18, REOL made their debut appearance in the music video for their track "Give Me a Break Stop Now". Despite this, the trio stayed anonymous with their identity, using anime-influenced illustrations and chibi designs to depict themselves several other animations were also distributed in their subsequent music videos. Subsequently, Reol, GigaP, and Okiku signed a record contract with Japanese label Toy's Factory, forming themselves as a unit under Reol's name-capitalized as REOL. It was released on Jthrough Victor Entertainment, and reached the top ten on the Oricon Albums Chart. Furthermore, Reol continued working on her debut studio album, titled Gokusaishiki. Reol and GigaP's first project as a duo was No Title, which was released on Augthrough Japanese label Celo Project. Additionally, Reol and art director Okiku had been long-time friends and occasionally collaborated with her music videos and packaging for her releases.

Reol and GigaP had consistently worked together prior to forming the musical unit REOL, providing compositions and vocals to several Japanese vocaloid acts such as Hatsune Miku. Furthermore, REOL had appeared on several promotional formats such as live performances, magazines and interviews on social media. In order to promote the album, the album tracks: "ChiruChiru", "Give Me a Break Stop Now", and "YoiYoi Kokon" were served as digital singles, accompanied with additional music videos co-created by Okiku. Several commentators complimented the group's musical direction, alongside Reol's vocals and commercial appeal.Ĭommercially, Sigma experienced moderate success in Japan, reaching the top ten on both the Oricon Albums Chart and Japan Hot Albums chart, the latter hosted by Billboard. Upon its release, Sigma received positive reviews from music critics.

Lyrically, the record delves into enjoyment, love, having fun and a variety of expressions, all encased by their current state of mind, as described by them as "transitory". Sigma is an electronic dance album that incorporates elements of hip-hop, contemporary pop and club sounds.

The material on the album were written, sung and co-composed by Reol, while production was handled by all three artists and arranged by Giga. Prior to their formation, each member- Reol, Giga and Okiku-worked with each other on numerous musical projects until finalizing a record contract with Toy's Factory in early 2016. It was released on Octoby Toy's Factory in two physical editions-a standard CD, and a CD and DVD bundle-and for digital consumption. Sigma (stylized with the Greek symbol Σ) is the debut studio album by Japanese musical unit REOL.
