不敗の戀人 (py. Bùbài de Liànrén, en. Undefeatable Lover) is an album by Taiwanese singer/actress/model Vivian Hsu, released on 18 October 1999 via the BMG label. Vivian's older sister Penny sang backup on some of the tracks, and later married the producer of this album.
Track 10 is a Japanese translation of track 3. Later, almost the entire album was translated into Japanese, and released in Japan as Fuhai no Koibito on 23 March 2000. Exceptions to the Japanese release are tracks 2, 3, and 6, which are original. In Taiwan, the Japanese album was released on the same day as Happy Past Days with a bonus disc with Mandarin Chinese versions of two of the three original songs, tracks 3 and 6.