The message will be brief.
"Game time," Johnson said.
The pair understand the stakes. They understand they will be tactically assessing each other in order to exploit any weaknesses.
"We know we're not friends on the court. There is going to be a battle, and we got to see who comes out on top," Johnson said.
Buck's listed height of six feet is slightly taller than the 5-foot-10 frame of Johnson, but state tournament followers have witnessed their athleticism transforming their respective teams.
"I don't expect anything chippy, but it will be bragging rights," said Red Wing head coach Dave Muelken. "They're just ultra-competitors."
The camaraderie will be visually discarded for 36 minutes, but gestures acknowledging their bond will appear as DeLaSalle battles for a third straight championship while Red Wing makes its first attempt at a title.
"Real best friends battle the best. They are not going to let each other have anything easy. You're going to see a great game from both of them," said DeLaSalle assistant coach Lisl Von Steinbergs.
The pair of seniors communicate with each other daily, often taking a moment to salute the successes of the other. Tabulating retweets between the two would be a challenging endeavor, but all fans need to know is how far their relationship extends.
"I would do absolutely anything for her. When I'm having a bad day, I go to her. When she's having a bad day, she comes to me," Buck said.
On game days, the interactions multiply.
"We text before every game, telling her what she needs to do and she tells me," Johnson said.
One of Johnson's "orders" came during the annual pre-tournament banquet on Tuesday, and Buck complied, bringing a few sweets with a personal message written on the package.
"There is a saying: game recognizes game. I think also game respects game," Von Steinbergs said. "As long as I've known Seanna, if she respects you, then she'll open up to you. She could be friends with the whole world if she opened herself up to that."
Similar to the relationship between the WNBA and foreign leagues, many players on the high school circuit encounter their brethren through AAU play, where rosters are frequently jumbled.
The rearrangement often allows high school prodigies to refine their game with players they usually compete against.
Buck and Johnson provide an example of how such refinement can lead to friendly results. They first met in AAU, playing for the prestigious North Tartan club in 2011. Observing their camaraderie, an unknowing patron could assume the two have played on the same team for a decade.
"We were just both so talkative. Me and her just found a bond," Johnson said, recalling her first meeting with Buck.
There was no communicative trigger, but one is not always necessary.
"Our personalities just clicked. We were good friends off the court, we had a feel for each other on the court," Buck said.
Both players crossed the 2,000-point barrier earlier this season, and both are headed to Division I colleges on basketball scholarships. Buck is playing for Wisconsin-Green Bay, a perennial feature among the "mid-major" colleges in Division I, and Johnson will take up residence at Iowa State.
Their season stats add another mirror, with Buck scoring 23.7 points per game for Red Wing and Johnson netting 22 points per contest. Johnson has the rebounding edge, averaging a double-double overall this season while Buck comes in at just under 10 per game.
Muelken illuminated the growing maturity of Buck through consecutive state tournament appearances. When Red Wing qualified in 2011, he believed the team was content with making the bracket, despite losing to Hill-Murray in the quarterfinal round.
In 2013, winning the section was deemed not satisfying enough. Buck and crew's only mission was advancing to Saturday's finals, and the renovated commitment led to upsets of New Prague and Richfield in the first two rounds.
"Even that first game, she looked under control and poised, whether she made a shot or missed a shot," Muelken said.
Similar to other participants in the bigger classes, the 18-year-old Buck relays her faith to teammates, no matter how a play results. Her trust eliminated potential frustrations in Red Wing's win over Richfield, when she fouled out with over three minutes left in regulation.
"She's going to get hers, but she's done such a nice job being a facilitator and creator," Muelken said.
Johnson has gained a sentimental following over the last two years through detailed coverage of her brother's heart attack and recovery. While the story contains the metaphorical storybook ending, Johnson's physical play to compensate for her smaller size at wing and power forward has hurt many opponents during her high school career.
"She has a quick first step, an eye as far as timing goes. Even though she doesn't really match up, she can pull any rebound that she wants," Von Steinbergs said.
The 17-year-old Johnson is one of DeLaSalle's reserved characters, preferring to chat through Twitter or texts. She is less shy about re-posting inspiring or intriguing messages directed at her, happily accepting words of support.
Johnson becomes extroverted when demonstrating her deceptively quick speed, which allows her to fix a potentially broken play.
"She's an extreme leaper, with hands like Spider-Man and the flexibility of Mr. Fantastic (Fantastic Four) to catch some things that are really uncatchable," Von Steinbergs said.
"She's the most unselfish player I know. She's my best friend, but I definitely look up to her," Buck said.
Saturday evening, Buck and Johnson will look directly at each other. They have never faced off as opponents before, and will never do so again in their high school career.
Eventually, the two will pass notes about their performance, as always. There may even be some smack talk. Anticipation is running high, but whoever wins, a mutual emotional high will follow.
"It's hard when you're playing your very last high school game against your best friend, but either way, I'm going to be happy," Buck said.