‘Half of my quarter of a century belongs to music, so I never belonged to anything else,’’ says Welsh songstress Duffy. ‘‘I feel very able and ready!’’ The blonde bombshell was in Tokyo for her first full-length live show in Japan — at Shibuya AX on March 17 — and is still basking in the success of her debut album, ‘‘Rockferry,’’ released in March 2008. Three BRIT awards and one Grammy later, the old-school soul singer is the lady of the moment, with 5.5 million album sales to her name.