Mitsubishi UFJ Financial Group plans to buy Japanese robo-advisory firm WealthNavi for as much as ¥99.7 billion ($665 million), as it looks to expand its financial-technology capabilities and cater to households going online to invest more of their savings.

Japan’s biggest bank is seeking to purchase WealthNavi through a tender offer at ¥1,950 a share and make it a wholly owned unit, according to a filing on Friday. That represents an 84% premium over the fintech company’s closing price on Thursday.

Japanese financial firms are expanding services to help households invest more of their $7.5 trillion in cash as inflation emerges in Asia’s second-largest economy. More people have been opening so-called NISA accounts following the expansion of the country’s tax-free investment program this year, helping to fuel a stock-market rally.