England begin an eagerly-anticipated summer with a one-off Test against Ireland at Lord's on Thursday, but already much of the discourse is around the upcoming series with Australia.
After a string of poor showings both on home soil and Down Under, the script book was ripped up this time last year when Rob Key, managing director of men's cricket at the England and Wales Cricket Board (ECB), decided to pair captain Ben Stokes and head coach McCullum together to revitalise red-ball cricket in this country.
The results were devastating with 'Bazball' taking the nation by storm with run-rates going through the roof, draws being discarded and the pressure of losing taken away, but the perennial question throughout England's run of 10 wins from 12 Tests has been, can it be taken into the high-pressure stakes of an Ashes series?
McCullum said: "It's a challenge, but it's an exciting challenge.
"The more that's at stake, the more it's important to keep it simple and relaxed, to do what gives you your greatest chance.
"At the first sign of trouble you can't run away from it, or at the first sign of all the eyeballs in the world watching you, you can't run away from what's been most successful for you.
"That's when you should be at your clearest, keep things as simple as possible and that will be the message right throughout."
Former New Zealand wicket-keeper McCullum is no stranger to battles with Australia, but modestly and perhaps unfairly suggested he was only good enough to scrap against teams wearing the baggy greens.
That is not the case for his England side, the 41-year-old insists.
"I'm not as good as these guys are, so you always felt like you were scrapping for something rather than being able to go toe to toe with them (Australia)," McCullum added.
"The ability to go toe-to-toe with a good side is where the magic happens.
"I think we've got the quality in our team and they've got the quality in their team to be a heavyweight contest so I'm excited about that.
"There's so much excitement about what's coming and there's so much uncertainty for everyone and that's where I think the real magic has the opportunity to come out. so we're just excited about it."
England's 'Bazball' approach has been heavily debated since it arrived on the scene and at its height, Stokes' side were scoring at 5.50 runs per over in Pakistan during earlier this year.
Whether or not that can be replicated remains to be seen, but McCullum does feel they should only get more consistent with time.
"To be fair, there's some stuff we did last year that I didnt really think was achievable but the guys were able to do it," he admitted.
"If you are present and clear of mind, you're able to make good decisions because you're not worried about the outcome as such, you're just able to adapt to what's required.
"There will be periods where we'll have to absorb pressure. It may also be that we'll be able to put the handle down a bit more and achieve what we did last summer. Well just wait and see."
A key part of England's philosophy is a relaxed environment and spending quality time together, which occurred on Sunday when the team linked up for the first time - since the New Zealand series in February - for a round of golf at the Grove in Hertfordshire.
After facing Ireland this week, England will have 11 days before the Ashes opener at Edgbaston on June 16, but that will not be spent exclusively together, with a mixture of days off, training and some "quality time" arranged before the battle for the urn begins.
McCullum stated: "I think it's a good build-up, I think its perfect."
One man not set to be involved is Ben Foakes after he was left out of the Ireland Test in favour of the fit-again Jonny Bairstow, who will don the gloves and try to replicate his stunning 2022 form where he hit six hundreds.
"Well, I mean he's an incredible player," McCullum said of Bairstow.
"He's a rare commodity and he's able to do some things that other people just can't.
"I think if he's able to recapture even a glimpse of the form which he showed last summer, then our side does look really, really strong."