SC Karuizawa Club won its fifth straight men's national title, defeating Sapporo 10-5 in Sunday's final and moving a step closer to the 2018 Winter Games.
In the women's competition, Chubu Electric Power won its first championship in three years, knocking off two-time defending champion LS Kitami 7-5 in the final.
Karuizawa, which was fourth at the world championships last year, will represent Japan at the Pyeongchang Olympics should it secure a top-seven finish at this April's worlds in Canada.
Sapporo led 3-2 after the third end, but Karuizawa scored two to restore the lead in the fourth, and three points in the seventh all but ended the contest.
"I was nervous. Everyone assumed we'd win and we did too," skip Yusuke Morozumi said. "But we could turn it into the kind of game we wanted to play despite going through a bad spell."
"We lost against them in the round-robin and I thought it'd be them if we were to lose," he added. "We've become the (prospective) Olympic representatives, so now we'd like to clinch the berth."
LS Kitami had beaten Chubu twice, but had the upper hand in the final, holding off the champions in a tense finish after Kitami threatened to come from behind.
"We'd played them twice and lost both times, so before this game we were talking among ourselves, saying the third time would be the moment of truth," skip Chiaki Matsuura said. "I made some weak shots and the sweepers covered for me."
In September, Chubu and LS Kitami will compete for a spot at the Olympics.