[1] Among his fellow pupils was Ryūsei Kishida, with whom Okamoto formed an artists' group and named it Fusain Society (Fyūzankai) to promote Post-Impressionism.

[1][5] Nevertheless, Okamoto and Kishida organized a new group together with Shōhachi Kimura and Kōtarō Takamura to give an exhibition of their own paintings in October 1913.

[1] In 1914, upon his marriage, Okamoto moved next door to Kusuyama Masao, a popular theater critic and translator of Western literature.

[1] Kodomo no Kuni was sold at a half yen per copy, relatively expensive compared to rival magazines, but was enough competitive due to its high quality of the pictures.

[9] In 1927, he participated in forming the Japan Association of Illustrators for Children with Takeo Takei, Tomoyoshi Murayama and other painters.