"Doughnut" is TWICE's 9th Japanese single, released December 15, 2021 via Warner Music Japan — their first Japanese ballad title track. The city pop-influenced song was produced by in-house JYP producer Woo S. Rhee "Rainstone" and lyrically explores the emotional void left by missing someone special, framed around the metaphor of a doughnut's hole. The MV, pre-released December 3 alongside the digital single, features a mystery-themed narrative set in an abandoned dessert shop, led by Mina. The physical release comes in four versions: Limited A (CD+DVD featuring jacket shoot making movie and member making video, 24-page lyric booklet, 1 of 9 trading card, serial number card), Limited B (CD, 4-page lyric booklet, 2 of 8 types photo sticker sheets, 1 of 9 trading card, serial number card), Regular (CD, 4-page lyric booklet, 1 of 9 trading card on first press, serial number card), and ONCE JAPAN fanclub edition (CD, 4-page lyric booklet, 3×3 fold poster, 2 of 9 trading cards, 2 serial number cards). The four-track release pairs the title with B-side "Wonderful Day" plus both instrumentals. It peaked at #3 on the Oricon Singles Chart and #6 on Billboard Japan Hot 100, and later appeared on the fourth Japanese studio album Celebrate.