Twenty-nine-year-old Yuki Yanagita is slated to earn his domestic free agent option some time next season. He reached an agreement on a three-year contract with the Softbank Hawks that will be worth an estimated 400 million yen (up 1.4 million yen from this year) plus incentives in 2018.
[UPDATE 12/24 @ 2:22pm]
There are some reports pointing to an estimated salary of 550 million yen plus incentives and a total contract that could be worth up to around two billion yen.
Assuming no major injuries, Yanagita could earn his international free agent option in 2020 (the last year of this current contract).
Source: Daily Sports 12/24/2017
[UPDATE 1/11/2018 @ 3:13pm]
Yanagita may have been offered up to five years, but went with three years because he is interested in exercising his international free agent option. He has apparently been asking the Hawks to change their stance on allowing players to go to the Majors through the posting system.
Source: Tokyo Sports 1/11/2018