TOKYO, May 14 (Reuters) - Japan's Rakuten Group on Tuesday logged an operating loss of 33.3 billion yen ($213 million) in the January-March quarter, its 15th straight quarter in the red as losses in its mobile unit weighed on robust growth in its fintech business.

The operating loss marks a strong improvement compared to a year earlier when the e-commerce and fintech group posted a loss of 76.2 billion yen.

($1 = 156.4800 yen) (Reporting by Anton Bridge; Editing by Tom Hogue)