During the March 23 Western League game with the Orix Buffaloes, he pitched 6 scoreless innings, giving up only 1 hit, and earned his first victory.

[11] He debuted as the starting pitcher on the April 2 Dragons match, where he pitched 5 scoreless innings, allowing 3 hits and a walk, while striking out three batters.

The Tigers scored 15-0 that day, giving him his first win on his first official match as a starter,[12] the 8th rookie to do so in franchise history.

He continued to appear in the Western League games, and on July 12, he earned a complete victory against Orix when only gave up 1 run in 9 innings.

But as the bullpen started to lose left-handed relievers due to injuries, Iwazaki was tasked to pitch in relief from September until the season ended.

[29] 2017 He started the season as a mainstay reliever, and together with Kentaro Kuwahara, Akifumi Takahashi and Marcos Mateo, they served as the setup men for the team's main closer Rafael Dolis.

Together with Kuwahara, Takahashi, Mateo and Doris, they made the Tigers become the first team in NPB history to have five pitchers reach sixty or more appearances in the same season.

[32] 2018 Even though their bullpen was short of southpaw starters, Hanshin still opted to use Iwazaki mainly as a reliever throughout the season.

2019 Despite suffering from left elbow pain early in the season, he brought his A-game in all his outings starting April 12.

[34] To make things worse, he also suffered from lower back pain so he did not return to the mound until June 19.

[40] But due to the season being delayed by the Covid-19 pandemic, he recovered in time to pitch in relief on his 29th birthday during the opening card with the Giants (June 19), which he unfortunately lost after giving up 2 runs.

[41] He redeemed himself in July when he notched a 0.84 ERA in 11 outings, but experienced tightness in his left elbow that inevitably got him sent back to the farms later that month.

[47] His unique delivery makes it difficult for the batters to assess the origin of the pitch, and his balls to have a later release point.

[48] When Iwazaki was in grade school, his father wanted to prioritize the proper development of his shoulders so he was made to join the swimming club.

He practiced all types of swimming styles that enabled him to train his legs, and at the same time, improved the flexibility of his arms and shoulders.