「テトリス」 (styled "TETORIS") is a Vocaloid original by producer Hiiragi Magnetite (柊マグネタイト), first released as a single in 2024 before entering SEGA's rhythm game ecosystem. The title is a deliberate portmanteau, fusing the name of vocal synth Kasane Teto (重音テト) with the classic puzzle game Tetris, rendered with the intentionally altered romanization "TETORIS" rather than the conventional "TETRIS." Musically, the track is a high-energy Vocaloid pop number at 170 BPM. Its most recognizable feature is the chorus, which directly quotes and reharmonizes "Korobeiniki" (コロベイニキ), the 19th-century Russian folk song that has served as the definitive musical identity of the Tetris franchise worldwide. Hiiragi Magnetite confirmed that the arrangement and rights clearance for the adaptation were properly secured. The vocals are performed by Kasane Teto SV, the Synthesizer V iteration of the long-running UTAU voicebank, delivering a bright synthetic tone that matches the song's frenetic lyrical themes, social anxiety, internet self-awareness, and self-deprecating humor wrapped in rapid-fire wordplay. テトリス debuted in rhythm games on CHUNITHM X-VERSE before arriving in maimai でらっくす CiRCLE on September 18, 2025, where it was released with a full set of five DX-standard charts plus a later UTAGE arrangement. The Re:Master chart (13.7 constant), designed by Luxizhel, stands as the most demanding at 941 notes, while the Master and Expert charts were handled by 緑風 犬三郎 and サファ太 respectively. The song later appeared in オンゲキ Re:Fresh, solidifying its status as a cross-title SEGA rhythm game staple.