Do As Infinity is a Japanese pop and rock band formed in 1999. The group was originally a trio consisting of vocalist Tomiko Van, guitarist Ryo Owatari, and guitarist and composer Dai Nagao. The band's name is sometimes abbreviated as DAI, a reference to Nagao. Signed to the Avex Trax label, they released their debut single Tangerine Dream on September 29, 1999. In December 2000, Nagao decided to devote his time exclusively to composing and songwriting and ceased appearing at live events and in promotional materials. The band released five studio albums between 2001 and 2005. Following the release of their singles compilation Do the A-side, Do As Infinity disbanded on September 29, 2005. The members pursued other projects, with Van beginning a solo career and Owatari working with his band Missile Innovation. The group reformed on September 29, 2008, as a duo consisting of Van and Owatari, with Nagao not returning.

The band has a notable history of contributing theme songs to anime series. One of their earliest and most successful anime tie-ups was Fukai Mori, which was used as the second ending theme for the popular series Inuyasha. Released in 2001, this song became a signature track for the band and helped expand their audience. They later provided another song for the same series, Shinjitsu no Uta, which served as its fifth ending theme. The band also contributed the song Rakuen to the 2004 film Inuyasha the Movie: Fire on the Mystic Island.

Years later, following the band's reformation, they were again connected to the Inuyasha franchise. Their twenty-second single, Kimi ga Inai Mirai, was released on January 20, 2010, and was used as the opening theme for Inuyasha - The Final Act. This single was a commemorative release that also included their previous Inuyasha theme songs Fukai Mori, Shinjitsu no Uta, and Rakuen.

A more recent anime collaboration came with the single Keshin no Kemono, released on December 6, 2017. This song was used as the ending theme for the television anime series Juni Taisen: Zodiac War. This single featured music composed and arranged by Hiroyuki Sawano, a notable figure in anime music composition, with lyrics written by Tomiko Van.

The music of Do As Infinity is primarily rooted in rock and pop, but their sound incorporates a range of influences, including alternative rock, jazz, and R&B elements. This diversity has allowed them to maintain a distinct musical identity over a long career. The band has released numerous studio albums, with early works such as Deep Forest (2001) and later albums like Eight (2011) achieving high positions on the Oricon charts. Their compilation album Do the Best (2002) was awarded the Rock & Pop Album of the Year at the 17th annual Japan Gold Disc Award. With a career spanning from 1999 to a hiatus in 2005 and a reformation continuing to the present day, Do As Infinity is recognized as one of Japan's significant musical acts, known for their enduring popularity and the distinctive voice of Tomiko Van.