Iwakuma, 31, recorded his first win as a Seattle starter with eight innings of one-run ball with 13 strikeouts against the Blue Jays on Monday, just two days after flying back from Tokyo.
Iwakuma, who will start against the Yankees' Freddy Garcia on Sunday, said his dad has been ill for some time and is not doing well. Being so far away is not an easy thing at this time.
"I understand what my father is doing right now," Iwakuma said Saturday through interpreter Daisuke Sekiba. "I expect he's going to be getting worse because of his illness. It's been two years.
"It's difficult, but I tried to do my best and just used the time with my father. Even if it was just a short time, it was useful."
Iwakuma said his father is too sick to talk on the phone any more, but he believes he's rooting him on as he pursues his first year in the Major Leagues.
"I didn't have much time to meet with him, but I think when I came to the United States, he's cheering for me every time from Japan," Iwakuma said. "It's hard for me to think about it."
The Mariners respect what Iwakuma is going through and know how tiring his trip to Tokyo must have been last week after making the same 13-hour journey themselves in March to play the A's in the Opening Series.
"He's a professional," manager Eric Wedge said. "He comes here to do his job. The personal side is so important, but he's able to separate. You can tell he's not a kid. He's a grown man, a family man. Mature, strong, tough. He has his priorities in order. There's a lot of experience there, not just as a baseball player but as a person, too."
Iwakuma, whose wife and two children are living with him in Seattle, has one wish now as he finishes out his first year in the U.S.
"I hope at the end of the season, I'll be able to see him again," he said. "During the season, I'm trying to do my best and show him what I can do to give him more energy. As soon as I finish my season, I want to go back home to see my dad one more time, if I can do it that way."