Gekkein (1568 - 1655) was a daughter of Yorizumi ASHIKAGA of the Oyumi Kubo family. Her names were Shimako, Himahime or Oshima. Initially, she was the lawful wife of the lord of Kuragasaki-jo Castle, Korehisa SHIONOYA. Later, she became a concubine of Hideyoshi TOYOTOMI.
Oshima was a Himegimi (daughter of a person of high rank) of the Oyumi Kubo family which was a branch family of Koga kubo family, Kanto Kanrei (A shogunal deputy for the Kanto region) and came from the most distinguished ancestry among Hideyoshi's concubines. Moreover, Oshima's first husband, Korehisa SHIONOYA was from a distingusihed family same as Oshima's Kizuregawa family, a descendent of MINAMOTO no Yoshiie and granted the territory of about 20,000 koku in Shioya-gun by MINAMOTO no Yoritomo.
In 1590, after the Siege of Odawara, when Hideyoshi came to Koga for Oshu Shioki (approach to punish the powerful warriors in the area of Oshu, to prevent them from strengthening their power), Oshima's husband, Korehisa fled, leaving her alone. After that Oshima who left behind met Hideyoshi, and became his concubine.
Oshima pleaded with Hideyoshi to rescure her family's home, not her husband's Shionoya family. Oshima asked Hideyoshi to let Kunitomo ASHIKAGA who was her brother and a grandchild of Yoshiaki ASHIKAGA and Ujihime ASHIKAGA, who was a daughter of Yoshiaki of the Koga kubo family marry, in order to revive the Ashikaga clan of the Kamakura kubo group which essentially became extinct because of the death of Yoshiuji ASHIKAGA (Koga kubo) in 1582. Hedeyoshi gave Oshima 3,800 koku of Kizuregawa as a dowry. It seems that Hideyoshi expected Ohima who came from a distinguished family to give birth to his children at the beginning.
In 1591, Hideyoshi acceded Oshima's request and let Kunitomo and Ujihime marry. However, Ujihime was so proud and nevertheless she lived in poverty with the fief of only 300 koku, she despised Hideyoshi who came from a poor family, saying that 'He is of low origin,' therefore, she was neglected by Hideyoshi for a time. Through Oshima's intervention, Ujihime was given 332 koku in 1590 and finally she could emerged from the poverty.