Japan's IPO volume reached 770 billion yen so far this year thanks to Dai-ichi's giant deal, compared with 28 billion yen a year ago, according to Thomson Reuters. data Otsuka is 12.4 percent owned by its founder and family members, according to an earlier company filing. The estimated offer price would value the company at more than 1.3 trillion yen ($15 billion), ranking Otsuka behind only three other drugmakers in Japan -- Takeda Pharmaceutical, Astellas Pharma and Daiichi Sankyo -- and roughly on a par with Eisai Co, Japan's No.4 drugmaker. The drug business traces its roots to the Japanese island prefecture of Tokushima, where founder Takesaburo Otsuka started a small chemical factory in 1921.