Japan's first startup unicorn is considering a new fundraising round to maintain momentum after a spike in U.S. downloads for e-commerce company Mercari Inc.

The company's free mobile app, which matches individual buyers and sellers, jumped to No. 3 in the U.S. download rankings last week, according to researcher App Annie. Daily downloads climbed tenfold to 300,000, bringing total installations in the country to 12 million, according to Mercari.

"We've passed a tipping point and the fire is beginning to spread," Chief Executive Officer Shintaro Yamada said in an interview in Tokyo this week. "How do we maintain momentum while keeping an eye on rivals and new markets? These are the things you consider when shifting gears. Additional fundraising may be necessary."