Detailed information about Fumio Okada's background and personality is not available from reliable sources. He is known to have been a member of the 7th Division of the Imperial Japanese Army, serving in a group alongside fellow soldiers Genjirou Tanigaki, a soldier named Tamai, and a soldier named Noma. He was equipped with an Arisaka Type 30 Rifle.

Okada appears in the Escape King Arc of the story. He is part of the squad that tracks Saichi Sugimoto and the Ainu girl Asirpa after they defeat and injure Superior Private Hyakunosuke Ogata. The group discovers the hut where Sugimoto and Asirpa stayed and follows their trail through the snowy woods. When they catch up to Sugimoto, who is unarmed and standing in front of a fallen tree that conceals a bear's den, Okada and Tamai briefly believe they may have the wrong person. However, when another soldier recognizes Sugimoto as Sugimoto the Immortal from the 1st Division, they realize he is their target.

As the soldiers prepare to shoot, Sugimoto deliberately jumps into the bear's den behind him. When the soldiers begin firing into the den, an enraged brown bear emerges. In the ensuing chaos, the bear attacks Tamai, who accidentally discharges his rifle, shooting Okada and killing him instantly. Okada therefore plays a minor role in the story, appearing only during this early pursuit sequence before meeting his end through accidental friendly fire. No information is available regarding any significant character development, notable abilities beyond standard military equipment use, or key relationships other than his status as a member of the 7th Division.