Kyle Korver was drafted into the N.B.A. late in the second round, in 2003, with little fanfare and low expectations. Over the past few seasons, however, the six-foot-seven guard, who resembles Ashton Kutcher, has become arguably the best shooter in the league, earning the delightful, Kanye-esque sobriquet Threezus. Korver holds the record for the highest three-point field-goal percentage in a single season (53.6, in 2010), and for consecutive games with a made three-pointer (a hundred and twenty-seven, in 2014). This season, he was named an All-Star for the first time. Now he's in the second round of the playoffs with the Atlanta Hawks, who are one win away from their first N.B.A. conference final.

Korver’s success has, predictably, been chalked up to genetics (his parents are both former basketball players; his mother once scored seventy-four points in a high-school game), practice (his dad estimates that Kyle has spent more than ten thousand hours on the court), and careful study of the game (the current Hawks G.M., Danny Ferry, has said, "He's very intelligent, very smart").

But it also has something to do, these past few seasons, with a Japanese ritual called misogi. According to Janine Sawada, a religious-studies professor at Brown University, the word misogi dates back to eighth-century Japan: it originally described a mythical taboo journey to the underworld, and, later, in medieval Japan, the painful but purifying deeds of ascetics, who would stand under waterfalls and chant for hours. Korver practices a decidedly modern version: "Once a year, you do something that you’re really not sure you can do."

Korver’s first misogi took place in September of 2013: he stand-up-paddleboarded from the Channel Islands, off the coast of Santa Barbara, back to the mainland, a twenty-five-mile stretch of open ocean where great white sharks are known to swim. Korver had paddleboarded only once before, and fell dozens of times in the waves before he figured it out, fine-tuning each stroke of the paddle as if it were his jump shot. With him was Marcus Elliott, a sports scientist and founder of the Peak Performance Project, who trains Korver in the off-season and introduced the concept of misogi to him earlier that summer. Elliott himself first heard about it two decades ago, from a judo-practicing friend at Harvard, where he was a medical student. For Elliott, the point of misogi is to "take on challenges that radically expand your sense of what's possible. There are just two rules: you have a fifty-per-cent chance of success at best, and it doesn't kill you."

Among Elliott's crew of philosopher-athlete friends in Santa Barbara, a few more rules of thumb have emerged: a misogi is a physical trial that you don't practice or prepare for (no marathons), you don't perform before a crowd (no CrossFit-style competitions), and you don't brag or pay to enter (no Tough Mudders). Thinking outside the box is important, too. "Does it make your jaw drop?" Elliott asked. "That's a good litmus test for whether something can be a misogi or not."

Last year, I accompanied Korver on his second misogi, while reporting a story for Outside magazine: a five-kilometre underwater relay with Elliott and two other friends in the shallows off Santa Cruz Island, without scuba gear, while taking turns carrying an eighty-pound rock. This, too, was something Korver had never done, but, over five hours, he mastered the mechanics and mindset needed to complete the task.

But how, exactly, does something like subaqueous rock-toting translate to the basketball court? Though Elliott prefers describing misogi as a "personal quest" that challenges both the mind and the body, it could also be lumped—however crudely—into the category of cross-training, which has long been utilized by N.B.A. players. During the 2011 lockout, Andre Iguodala, then a Philadelphia 76er, took up boxing. The Hawks backup point guard Dennis Schröder skateboards, which helps him with balance. And it's well known that Kobe Bryant loves soccer, which is great for footwork. But cross-training is also crucial for staying healthy over a season and into the playoffs, which can be a challenge with the current N.B.A. schedule, particularly for older athletes. (Korver is thirty-four.)

"An eighty-two-game season is more of a grind than anything I've ever been a part of,” Korver wrote in an e-mail. “There are so many highs and so many lows ... Days when I love basketball and days when I'd rather kick the ball then shoot it.” In recent years, a number of star players have pushed for the league to shorten the season. Until then, Korver says that he will rely on misogi to help endure what can otherwise feel endless: “Sometimes you look at the schedule and you're not sure you're gonna make it. Those are the days when you have to call on your grind mode. Misogis have turned into my grind activator."

Despite earning the top seed in the Eastern Conference, the Hawks struggled against the Nets to make it to the second round. They are now in a tight series with a fifth-seeded Washington Wizards squad that lost its best player, John Wall, to injury for two games. Other teams have also, at least briefly, lost important players in this year's war-of-attrition-themed playoffs: the Cavaliers' Kevin Love (shoulder), the Grizzlies' Mike Conley (face), and the Bulls' Pau Gasol (hamstring) have all gone down for a game or more. Aside from a case of the flu, the Hawks starters have all remained healthy this postseason. So why the slow start?

"The playoffs are even more mental than physical," Korver explained recently by phone. "There are a lot of emotional games. Lots of tight games. We were fortunate to use the last few weeks of the season for rest, because we had a little lead in the standings. But we kind of lost a bit of our edge. We've been trying to find that again lately."

On Wednesday, the Hawks pulled out a much-needed win against the Wizards, which put them up 3-2 in the series. Korver was smothered by Bradley Beal for most of the contest and didn't shoot well, but, with fewer than five minutes remaining, he managed to hit a deep three that kept the Hawks in the game. I imagined him mouthing the words "grind mode" as it went in.

A naturally reserved and self-effacing person, Korver hasn't mentioned misogi to his teammates. He only brings it up if you ask. But, when you ask, he'll wax poetic. “Misogi becomes part of your DNA, an insurance policy for your mind,” he told me. “You look at things differently: focus on details and try to do them well, stay consistent. If I'm struggling on the court, I can think back on running rocks underwater for inspiration.”

Korver's sights are set on helping the Hawks reach the N.B.A. finals this season. But that hasn't stopped him from imagining a new challenge with Elliott and the misogi crew. The subject of a recent e-mail thread between them read, “Next misogi: Let's climb Everest . . . in a stairwell.” E-mails flurried back and forth for a few days about the where, when, and how of the epic stair climb. Eventually, Korver chimed in: "Was talking to a good friend the other day," he wrote. "He asked about next misogi. I told him [the] stair idea. He said that there is actually a stair racing tour. His buddy is on it. He has sponsors. Wins money. He took 3rd in Hancock tower race last month in Chicago. Made it in a little over 10 minutes. Interesting!"

Of course, they'd do it with no one watching. Maybe up and down the tallest tower in the world, in Dubai, if they can get access. The misogi crew has been crunching some numbers and, assuming members can maintain an ascent rate of twenty seconds per floor, they could climb the equivalent of Mount Everest in under fourteen hours.