Mercari Inc., Japan's first startup unicorn to go public, made its much-anticipated debut Tuesday on the Tokyo Stock Exchange's Mothers section, becoming the largest initial public offering so far this year.

Shares of the flea market app operator started their first day of trading at ¥5,000, up 67 percent from the initial offering price of ¥3,000. This put its market capitalization at more than ¥670 billion, making it the largest company on the Mothers market for startups, surpassing smartphone game-maker Mixi Inc.

"Through this IPO, we aim to push forward our effort to become a global-level tech company," Shintaro Yamada, founder and CEO of Mercari, said at a news conference after the bell-ringing ceremony Tuesday.