TOKYO -- It’s one thing to make your Major League debut. It’s quite another to make your Major League debut in the Tokyo Dome.

Either option is a once-in-a-lifetime deal, but the double-bonus points for a debut in Japan puts things over the top for four Mariners this week in Tokyo.

Outfielder Braden Bishop, utility man Dylan Moore and Rule 5 rookie reliever Brandon Brennan are all in position to make their first MLB appearances if they get into action in the Opening Series against the A’s on Wednesday or Thursday.

You can add Yusei Kikuchi to that mix as well when he starts Thursday’s game on the mound, though Kikuchi pitched twice in the Tokyo Dome during his time with the Seibu Lions in Japan before signing this winter with Seattle as an international free agent.

When Kikuchi wrapped up his final season with Seibu, he never dreamed he’d be back in Tokyo so soon as the first Japanese player ever to make his MLB debut in Japan.

“Last October, when we lost in the postseason, I didn’t think I was going to pitch in Japan ever again, so I’m very excited for this opportunity,” he said. “I never imagined this. A few months ago, I had no idea. This opportunity will be once in a lifetime. I hope I can make my contributions and perform well.”

For the three American rookies on Seattle’s roster, none had ever even been to Japan before boarding the Mariners’ 12-hour charter flight around the globe last Thursday.

“When I dreamed about it, I didn’t think it’d be in Japan,” Bishop said of his MLB debut. “But I’ll take it anywhere.”

Brennan made the club after his selection from the Rockies in December’s Rule 5 Draft and will become the first Rule 5 pick to make Seattle’s Opening Day roster since lefty reliever David Rollins in 2014. It’s not an easy path and Brennan isn’t your typical young Rule 5 pickup as a 27-year-old with only 18 games pitched in Triple-A.

But Brennan only converted to the bullpen two years ago and the Mariners’ analytics department identified his changeup – a pitch he changed his grip on about a year and a half ago to new-found results – as a potential difference maker. So he’s getting his shot, beginning with the trip to Tokyo.

“I’m just taking it in and enjoying myself, just kind of getting around and seeing how Tokyo is,” said Brennan, a California native who spent one year at the University of Oregon in 2011 before being drafted by the White Sox. “The baseball aspect, I’m just getting along with the guys and hanging out. I haven’t really thought a whole lot about it. I don’t think it has really set in, to be totally honest.”

For the first-timers, it’s been a whirlwind week. First came the news they’d made the travel roster to Tokyo. Then the rush to get ready, the 5,000-mile flight to Japan and now the reality that they’re actually in the big leagues and getting ready to play regular-season games against the A’s.

It’s all a foreign experience, particularly in a foreign country. But adapting to new situations and challenges is part of the life of any Major Leaguer and this is just the beginning, if all goes well. Though having been around baseball, these youngsters know better than to take their situations for granted.

Bishop has never played above Double-A ball, but the former University of Washington standout earned his roster spot by performing extremely well this spring after center fielder Mallex Smith was sidelined by a strained right elbow.

He knows his status is far from guaranteed once Smith is healthy, which could be as soon as the club returns to Seattle for its home opener on March 28. Which is why Bishop is still balancing the word from manager Scott Servais that he’d made the team.

“I was in shock when he first told me,” said the 25-year-old. “It’s something you work for your whole life and put in so many hours that nobody sees. It’s just kind of the ‘I made it feeling.’ But then I’m like, ‘OK, now I have to figure out how to stay.’ That’s always going to be a challenge, trying to stay and establish yourself. It’s that constant challenge. But obviously it’s an enlightening time.”

Like all the newcomers, Moore is trying his best to take his Major League debut in stride. But that will be easier said then done once the Opening Day ceremonies begin.

“I’m just trying to think of it like I’m playing with the same guys I’ve played with for the last month and a half,” he said. “I’m just trying to keep my cool so I can play under pressure. It’s the same game. They throw a little harder, that’s all.”

Moore, 26, couldn’t imagine a better way to break into the big leagues after four years in the Minors, topping out at Triple-A last year for the Brewers.

“It’s been awesome. It’s been insane,” he said after coming off the bench in right field in Saturday’s exhibition game against Yomiuri. “The stadium, the people, where we’re playing. This is the big leagues for me. This is crazy. Playing in front of all these people was amazing.”

Like all the newcomers, Moore is trying his best to take his Major League debut in stride. But that’s easier said then done once the Opening Day ceremonies begin.

“I’m just trying to think of it like I’m playing with the same guys I’ve played with for the last month and a half,” he said. “I’m just trying to keep my cool so I can play under pressure. It’s the same game. They throw a little harder, that’s all.”