He was born in 1592 in Joseon.
Hidenari participated in the Imjin war. In 1597, he heard the crying near his camp in Suwon, and his retainer found a child by the river. The appearance of the child was so “uncommon” and “friendly” that Hidenari invited him. A prisoner said he was the son of 曾清官, commanding officer of Joseon who led 500 soldiers, but his name was still unknown. Hidenari felt pity for him, and decided to raise him in the camp. Hidenari named him Seikan (清官) using the same character of his father.
In the following year, Hidenari returned to Japan with Seikan. Seikan stayed the residence of Hidenari in Osaka for a few years.
In 1601, Seikan moved Hidenari's territory, Bungo province. Seikan became the retainer of Hidenari because his personality and descend was appreciated. He was given the surname Soga(曾我) which resembles his father's one, 曾. He worked alongside and pleased Hidenari. After a time, he was given the salary and became the page of Hidenari.
It is unknown of the date, and month he was born in. And even the year of which he died on and how he died.
- 内藤 雋輔 (1976), 文禄・慶長役における被虜人の研究, 東京大学出版会723頁
- 内藤 雋輔 (1976), 文禄・慶長役における被虜人の研究, 東京大学出版会723-724頁
- 内藤 雋輔 (1976), 文禄・慶長役における被虜人の研究, 東京大学出版会724頁