After I Married Orion, I Went Crazy on the Mountain.

[Era + space + farming and hunting + single female protagonist + decisive killing] A modern fisherman failed to fight against the giant monster. Once he traveled back to 1959, he became a migrant family member of the decentralized "rightists". At the beginning, he encountered the only daughter of Orion. After being forced to marry into a married woman, he hunted, farmed, raised his family, and occasionally helped the security team catch bad guys hiding in the mountains. Slowly, the whole mountain became his back garden!