A long-awaited new single from anime song singer and singer-songwriter Azuna Riko, released after a year's absence. This work was also written and composed entirely by Azuna herself, with the lead song "Horizon" arranged by Takahashi Hibiki. The song is centered around a danceable four-on-the-floor beat track, and features Azuna's delicate acoustic guitar sounds, making it a new frontier for Azuna Riko, who has stuck to dance music and anime songs. It was also performed as the lead song on Azuna Riko's "Road to Horizon" tour, which began in February this year, and has become a song that is rapidly gaining popularity among fans. The B-side "Unheard Voice" is an emotional song that makes full use of the solid sound of the acoustic guitar and features Azuna Riko's soulful vocals. All of the acoustic guitar parts, both solo and backing, are played by Azuna Riko herself, fully demonstrating her skills not only as a singer-songwriter but also as a guitarist.