It took a while for Junichi Yasuda to realize that he had a winner on his hands. In August, the filmmaker’s low-budget feature “A Samurai in Time” opened at a single theater in Tokyo. A comedy about a 19th-century warrior who finds himself transported to present-day Japan, the movie had been warmly received at Montreal’s Fantasia Film Festival the previous month. Local audiences seemed to like it, too.

Yasuda’s phone was buzzing with messages, but he didn’t let that go to his head. When a screening sold out, he figured it was because the cast and crew were making a stage appearance, or because tickets at the theater — Ikebukuro’s Cinema Rosa — were discounted that day.

But the momentum kept building. In short order, “A Samurai in Time” expanded to a second cinema, then to more than 50. Film distributor Gaga stepped in to take charge of the theatrical rollout, and by October the movie had broken into the box-office top 10.