Kodai Senga told reporters on December 27 that he spoke to the Softbank Hawks about wanting to be posted to the Majors before he earns his international free agent option during salary negotiations on December 21. He said he never really considered playing in America until recently (he enjoyed pitching at the World Baseball Classic where he went 1-1 with a 0.82 ERA, sixteen strikeouts, one walk, and seven hits over eleven innings of work spanning four games). The Hawks are not known for posting their players, so it is uncertain what they plan to do with Senga’s request. As of now, the twenty-four-year-old pitcher is not scheduled to earn his international free agent option until some time during the 2022/2023 season.
[UPDATE 1/13/2018 @ 5:15pm]
Senga is not necessarily interested in being posted to the Majors before he earns his free agent option. According to Tokyo Sports, he merely wanted to let the Hawks know that he has a desire to play in the Majors. He also wanted them to give him a place to express his feelings.
Senga could have kept his discussions with the team private, but decided to make them public because he wanted the additional pressure to perform.
Source: Tokyo Sports 1/13/2018