Ayumi Morita secured a berth in the Fed Cup World Group next season when she defeated Tamaryn Hendler to give Japan an insurmountable 3-0 lead over Belgium on Sunday.
It will be the first time since 2007 that Japan will return to the elite eight-team World Group.
The 22-year-old Morita, who gave Japan a 1-0 lead by beating teenager Alison van Uytvanck in the opener on Saturday, notched up a 7-5, 6-2 victory over Hendler, Belgium's top player this week.
On Saturday, veteran Kimiko Date-Krumm, former world number four, defeated Hendler 6-1, 6-4 to make it two up for Japan.
Nara Kurumi replaced Date-Krumm for the dead singles rubber in the fourth match against van Uytvanck, followed by a doubles with Morita teaming up with Rika Fujiwara against Ysaline Bonaventure and An-Sophie Mestach.
Belgium will be relegated to World Group II next season.
Belgium missed former world number one Kim Clijsters, who has a torn hip muscle, and the country's highest-ranked player Yanina Wickmayer, who wanted to concentrate on the WTA Tour.