LOUISVILLE, Ky. — Inevitably, there will be a moment on Sunday when Creighton’s Arthur Kaluma, a silky, skilled, 6-foot-7 sophomore, is isolated against San Diego State’s Adam Seiko, a compact, rugged, 6-foot-3 senior, each desperately intent on taking his team to the Final Four for the first time.

It won’t be the first time they will have locked eyes and fiercely attacked each other.

They are, after all, brothers.

“Surreal,” said Kaluma, who watched from the tunnel as Seiko delivered the go-ahead 3-pointer in San Diego State’s upset of top-ranked Alabama, and then helped Creighton fend off Princeton in the South Regional semifinals. “It’s an amazing experience, watching my brother play and then having the chance to play against him — especially at this level.”

What is most fantastical is that the brothers, and their family, went through this last year, when Creighton rallied from a 9-point deficit in the final two minutes and beat San Diego State in overtime in a first-round game in Fort Worth.

That game took place not far from the Coppell Family Y.M.C.A., the gym near their former home in Lewisville, Texas, where Kaluma left several impressions on his big brother.

It is the court where Kaluma beat Seiko for the first time playing one-on-one, and also where Kaluma, who is five years younger and four inches taller, head-butted his older brother on a drive to the basket, opening a gash that left a half-inch scar on Seiko’s left eyelid that took nine stitches to close.

“I think you can still see the scar,” Seiko said on Saturday, closing his eye and offering up a clean view of it for reporters who were gathered around.

The brothers carried on, well, like brothers. They are immensely proud of each other, but also made sure that the other knew his place. As each of Kaluma’s boastful pronouncements — that his brother can’t guard him, that Creighton will win again — were relayed to Seiko, he rolled his eyes.

“He’s just trolling me,” Seiko said.

As for what happened last year?

“I don’t want to hear no excuses about how you guys had us or anything like that,” Kaluma said late Friday night. “We won the game at the end of the day. Now, they’ve got a chance to even the score, so we can’t let that happen. Got to be 2-0 over my bro.”

Sibling rivalries taking a national stage seems to be a thing lately.

In this year’s Super Bowl, Philadelphia center Jason Kelce and Kansas City tight end Travis Kelce played against each other when the Chiefs beat the Eagles. They never lined up head-to-head, but the Nola brothers did in last October’s National League Championship Series as San Diego catcher Austin delivered a key hit against his brother Aaron, a Philadelphia pitcher. It helped the Padres win the game, but the Phillies took the series.

There will be no such consolation prizes on Sunday.

Afterward, the brothers’ parents, Patrick and Eva Ariko, and their two young sisters, Abigail, 10, and Anna, 8, will take turns comforting the loser and celebrating the winner, just as they did a year ago. They have tickets for Sunday’s game in both the San Diego State and Creighton sections, just as they did last year when they switched seats at halftime.

“This year, we may just go neutral,” said Patrick with a laugh. “Plain white T-shirts and go sit way up in the bleachers.”

Patrick immigrated to the United States from Uganda in the mid-1980s because he no longer felt safe after a change in power. “I was identified as someone who could be groomed to work against my tribe,” he said. Having settled in the Los Angeles area, he met Eva at a Ugandan community wedding. By then, she had two boys — Adam, with whom she was pregnant when she came to the United States from Uganda in 1998, and Arthur, who was less than a year old.

“I was smitten,” he said.

“Patrick and I were meant to be,” said Eva, who married him in 2008, and moved to Dallas and then near Phoenix, where they now live. “For him, it’s always been, ‘I take you with everything you come with.’”

Patrick had introduced the boys to soccer when they were growing up, but Adam soon was bitten by the basketball bug and Arthur followed along, impatiently running onto the court with a basketball during any timeout or halftime break during Adam’s youth games.

As he got older, Arthur watched his older brother — the diligence with which he studied the game and worked in the gym. When he was in middle school, Arthur asked Adam to help improve his ball handling. So Adam set up a series of cones for a dribbling drill in the front yard of their home in California.

“Every time I’d mess up a drill more than three times, he’d just walk out and go, ‘Man, you’re never going to get this,’” Arthur said. “At a young age, that kind of hurt.”

But Arthur kept at it, and while Adam was on his way to San Diego State, Arthur sprouted up, shooting past his brother by the time he entered high school. Soon, they began playing competitive games against each other — and Arthur’s indomitable self-confidence had found a receptacle in which to take root.

At what age did he think he could beat his brother?

“Ever since I first picked up a basketball, I thought I could beat him one-on-one,” Arthur said. “There was never a question of, ‘Oh, maybe just get me a couple years.’ It was, ‘No, I can beat you now.’”

Before they played last year, Arthur told reporters that his brother played fake defense, like Patrick Beverley, a notorious N.B.A. pest. And after Arthur drew a double team — and a foul — when he posted up Adam in last year’s game, he has reminded Adam that he needed reinforcements to reign him in.

“Even though Arthur is feisty, he looks up to his brother — a lot,” Eva said. “It’s beautiful to see.”

Said Patrick: “Adam’s been good as an older brother. He understood where Arthur is and not kill that competitive spirit but rather nurtured it and managed it.”

In many ways, both brothers are avatars for the teams they have helped get to this point. Adam, a sixth-year player, is a dependable role player off the bench, who is asked to shoot 3-pointers and defend for the oldest team remaining in the N.C.A.A. tournament. Adam is a more freewheeling wing and one of three sophomores who start for the high-octane Bluejays.

Their mother said that when she takes her seat on Sunday, it will be with a great deal of pride, and she expects memories of the kids playing out in the front yard with a little mini-basketball hoop to come flooding back.

Some of those thoughts rushed in on Friday night.

For all the brotherly gibing, when San Diego State finished off its upset, Arthur bolted onto the court to celebrate with his family and then have a moment with his brother, before he took the court to play Princeton.

Adam hugged him, wished him good luck and also had a message: “You guys better be ready.”