Lunar Mare is a high-energy instrumental boss track that originated in Rayark's mobile rhythm game Cytus II, later ported to maimai でらっくす PLUS as part of a cross-company collaboration between Sega and Rayark released on June 11, 2020. The song pits two titans of the doujin and BMS (Be-Music Source) scene against each other: xi (Yusuke Ishiwata), renowned for genre-defining compositions like "FREEDOM DiVE" and "Parousia," and sakuzyo (Mitsuki Yoshida), celebrated for emotionally charged works such as "Altale" and "AXION." Their combined output delivers a driving, synth-heavy instrumental at 165 BPM that balances xi's technical complexity with sakuzyo's melodic sensibility, a sound that fits naturally into the GAME & VARIETY category while carrying the prestige of the Cytus series. In maimai, Lunar Mare is represented across four DX-format difficulties, with the MASTER chart (level 13+, constant 13.8) designed by シチミヘルツ (Shichimi Hertz) and the EXPERT chart (level 11+, constant 11.6) by サファ太 (Safata). The MASTER chart in particular stands out for its dense 896-note count, including a substantial 80 Touch notes and 46 Break notes, making it a demanding full-board workout. Lunar Mare has undergone a few level adjustments across maimai versions: its BASIC chart was originally level 6 before being lowered to 5, and the EXPERT chart was later raised from 11 to 11+. Regionally, the song was released simultaneously across Japanese, international, and USA versions, with staggered rollout in Asia (November 2020) and China (May 2021 on 舞萌DX 2021), though it was later removed from Chinese cabinets beginning with 舞萌DX 2022.