Japan qualified for the Fed Cup's top-tier World Group when Ayumi Morita beat Belgium's Tamaryn Hendler 7-5, 6-2 in Sunday's reverse singles.
Morita's win at Ariake Colosseum gave Japan an insurmountable 3-0 lead in the World Group playoff.
Morita beat Alison Van Uytvanck 6-4, 6-4 in the first match on Saturday and Kimiko Date-Krumm overpowered Hendler 6-1, 6-4 in the second match.
Japan will return to the eight-nation World Group for the first time since 2007. Belgium will be relegated to World Group II.
Belgium was playing the series without its top three players - Yanina Wickmayer, four-time Grand Slam champion Kim Clijsters and Kirsten Flipkens.
''The Belgians didn't have their best players but we did what we needed to do,'' Morita said. ''I'm relieved that I won.''
Van Uytvanck defeated Kurumi Nara 7-6, 6-0 in the dead fourth rubber to give Belgium a consolation point. It was 18-year-old van Uytvanck's first Fed Cup victory.
