冬のこもりうた (Fuyu no Komori Uta) is a gentle pop ballad performed by Tomoyo Harada, a veteran Japanese singer-actress whose career spans from the 1980s idol scene to contemporary film and music. The song was composed and arranged by Goro Ito with lyrics by Kumiko Takahashi, and originally appeared on Harada's 2019 album Candle Lights before being selected as the main theme for the 2019 animated film 映画すみっコぐらし とびだす絵本とひみつのコ (Sumikko Gurashi: The Secret of the Flying Picture Book). The title translates to "Winter Lullaby," and the track's warm, understated arrangement, built around piano, gentle strings, and Harada's soft vocals, mirrors the cozy, nostalgic atmosphere of the Sumikko Gurashi franchise. In maimai DX, 冬のこもりうた was added as part of the Splash PLUS update on March 18, 2021, available in both Japanese and Asian region cabinets from launch day. Its chart set spans a wide difficulty range: a Basic chart (level 1) that any player can clear, an Advanced chart (level 5), an Expert chart (level 7+) designed by Jack, a Master chart (level 10+, constant 10.6) designed by 緑風 犬三郎, and a demanding Re:Master chart (level 13, constant 13.0) also designed by Jack. The Re:Master chart packs 388 notes into its 1:52 runtime, with a notably high density of Slide (62) and Touch (51) notes that create a technical challenge at odds with the song's gentle lullaby mood. The song was removed from all maimai DX versions on September 14, 2023, and from the Chinese edition (舞萌DX) with the arrival of 舞萌DX 2023, making it a retired track that can no longer be selected in current arcade releases.