Splash Dance!! is the main theme of ONGEKI SUMMER PLUS, composed by the prolific production unit Q-MHz and performed by ONGEKI Shooter's, a collective name for the five main heroines of Sega's ONGEKI rhythm game: Akari Hoshizaki (CV: Hikaru Akao), Rio Takase (CV: Yurika Kubo), Haruna Sakurai (CV: Reina Kondo), Koboshi Inohara (CV: Haruna Momono), and Chinatsu Hinata (CV: Miho Okasaki). The arrangement was handled by Q-MHz alongside yashikin (Kouta Kobayashi), both regular contributors to Sega's arcade rhythm game soundtracks. Brought to maimai as part of the ONGEKI & CHUNITHM crossover category, the song arrived in maimai DX Splash PLUS on September 3, 2021, with availability across Japan, Asia, the United States, and China. It later appeared in CHUNITHM NEW PLUS in July 2022, completing a full-circle crossover across Sega's three arcade rhythm families. The track runs at a consistent 155 BPM and has a play time of 2 minutes and 32 seconds. Lyrically, the song leans fully into a high-energy summer atmosphere, urging listeners to dance through the heat, eat ice cream, and seize the season's excitement. Its MASTER chart (level 13, constant 13.4) was designed by はっぴー and is notable for a playful gimmick in the lead-up to the second chorus: a sequence of Slide notes that trace the letters "S", "p", "l", "a", "s", "h" across the screen. The EXPERT chart was designed by サファ太.