トレジャーガーデン (Treasure Garden) is the fourth installment of Project ONSOKU, a cross-company collaboration between Sega's Sonic the Hedgehog franchise and the virtual singer Hatsune Miku. The track was composed, arranged, and written by Ponchi♪, with Hatsune Miku providing the vocals. Its music video was created by the artists ヨワネヒトリ and 夢ノ内. The song premiered simultaneously in maimai DX CiRCLE and CHUNITHM X-VERSE on November 20, 2025, and arrived in オンゲキ Re:Fresh the following month. Lyrically, the song paints a cheerful garden metaphor, picking shiny fruits, planting seeds, and watering flowers as acts of spreading love and happiness. The chorus's repeated refrain of "そしたらさ きっとHAPPYじゃん" ("then surely it'll be HAPPY, right?") captures the track's bright, infectious optimism. Running at 268 BPM with a length of 2:35, the song's high energy and playful melody reflect both the whimsical Chao creatures from Sonic and the lively VOCALOID pop style that fans of niconico-associated tracks will recognize. In maimai, the MASTER chart (level 13.8, designed by アマリリス) features over 1,050 notes with dense patterning, while the EXPERT chart (level 11.6, designed by Luxizhel) offers a demanding gate before the top difficulty. The song carries a niconico & VOCALOID genre tag in maimai and is available across Japanese, international, and North American regions.