One theory holds that after the Battle of Yamazaki, she had relied on Chosokabe Motochika, her uncle, for help, and had spent some time at Oko Castle in Tosa province Because Fuku was a woman, she was spared execution and was raised by her maternal relative, aristocrat Sanjonishi Kinkuni.

[1] In 1600, during the Sekigahara campaign, Fuku's husband, Inaba Masanari, served Kobayakawa Hideaki in the Western army led by Ishida Mitsunari.

After Hideaki joined Ieyasu, Mitsunari's army was defeated, as a result of which the Fuku family obtained a large amount of spoils of war.

They say that Fuku's excellent pedigree, refined and aristocratic education and the military exploits of her ex-husband Masanari were all positive factors in her selection as a wet nurse.

During her lifetime she accumulated high political prestige, being responsible for numerous negotiations with the Imperial court, maintenance in the shogunate cabinet, hiring officials and stabilizing the Ooku system.

In 1629, when Iemitsu was stricken with smallpox, she visited Ise Jingu Shrine to pray that he would be cured, Ofuku (Kasuga) traveled to the capital her way back where she had an audience with the Empress Meisho and Emperor Go-Mizunoo at the Imperial Court in Kyoto.

According to tradition, Lady Kasuga and Empress consort Tokugawa Masako (Oeyo and Hidetada's daughter) broke a taboo by visiting the imperial court dressed as commoners.

After the death of Oeyo (Iemitsu's mother), Kasuga no Tsubone exerted herself to the utmost to find consorts for him, convincing a succession of women including Eikoin, the abbess of Keiko-in Temple in Ise Province, as well as Hoju-in and Junsho-in, to enter the Ooku.

The poem she wrote upon her death reads, "As it sinks into the West, the moon beckons me to transcend the law; today at last, I shall surely escape the Burning House (a Buddhist metaphor for the current world of passions and agony)."