Following the Meiji Restoration of 1868, Japan went through a period of rapid modernization, and many were sent to the West to bring back knowledge and technology.

The government agreed to it, and he set off for Norway, where he purchased whaling equipment at 10% above the prices asked to ensure early delivery to Japan.

[3] Oka returned to Japan and in Yamaguchi Prefecture on 20 July 1899 established the whaling company Nihon En'yō Gyogyō K.K., nicknamed the Ichimaru Kaisha after its logo: the Chinese character for the number one (一 ichi) within a circle (maru).

Oka's was not the first modern whaling corporation in Japan: Hogei Gumi had preceded it by a year, but had found little success and closed in 1900.

[3] Japan was in financial straits following the First Sino-Japanese War (1894–95) so Oka found it difficult to raise the 100,000 yen necessary for the enterprise.

The company applied for a whaling licence from Korea, which was difficult to obtain as the Korean court was under the influence of the Russian Empire.

Nihon En'yō Gyogyō faced near ruin when the Daiichi Chōshū Maru was wrecked on the coast of Korea in a blizzard on 2 December 1901; the ship was uninsured, as no insurance company had been willing to cover it.