Imai can make up to $63 million with incentives. He was offered longer deals with a lower annual average value, but opted to go with the Astros on a shorter deal with higher earnings per year, according to MLB insider Mark Feinsand.
The 27-year-old is coming off a career year with the Saitama Seibu Lions, tossing a 1.92 earned run average with 178 strikeouts through 163.2 innings.
He threw five complete games, three of them shutouts, and gave up just 101 hits, 48 walks, and six home runs.
Imai, a three-time NPB All-Star, was the coveted No. 1 international pitcher free agent this offseason, following the trend of high-end Japanese starting pitchers after Yoshinobu Yamamoto and Roki Sasaki signed with the Los Angeles Dodgers - a team he adamantly didn't want to play for.
“I want to beat them… beating a team like that and becoming world champions would be the most valuable thing in my life," said Imai.