Christophe Weber says growth and innovation are the metrics for success in Takeda Pharmaceutical Co.'s $62 billion purchase of Shire PLC. The first order of business is bringing global shareholders around to Japan's biggest-ever outbound takeover.

The Takeda CEO is facing a 21 percent drop in the stock price since the company disclosed its interest in March, while Shire is trading £9 ($12) below the offer price of roughly £49 a share. He's also contending with some domestic shareholders who are averse to expansion as Weber looks to create a global pharmaceutical giant.

In an interview at Takeda's new Tokyo headquarters, the French-born CEO discussed his push to sell the deal overseas — and in Japan — and plans to integrate the 237-year-old drugmaker with a London-listed company with mostly U.S.-based operations.