Eddie Jones told England on Thursday "you never know what can happen on a hot day" as he plots to beat his former team at the start of his second stint as Japan head coach.
The feisty Australian named his squad for Japan's summer test matches, which start with a showdown against Steve Borthwick's England at Tokyo's National Stadium on June 22.
Jones led England to the 2019 World Cup final before being fired three years later and returning to Japan via a disastrous spell in charge of Australia.
The 64-year-old said he had been getting "a feel for the landscape" since starting work at the start of the year and was raring to lock horns with England.
"We know what they'll bring. They'll bring a strong kicking game, strong set-piece game," he said of England.
"It's going to be a great challenge for us to play against them, and we're going to have to play really well.
"But you never know what can happen on a hot day in Tokyo."
Jones has set Japan a target of reaching the semifinals for the first time at the 2027 World Cup in Australia.
They exited in the first round at last year's tournament in France under Jones's predecessor Jamie Joseph.
Jones said "every day counts" as he prepares to take his players into a training camp for the first time.
"First six months in the job, you do a lot of watching, a lot of learning, talking to coaches, watching as many games as you can," he said.
"To get the players in the camp, even for an old coach like me, it will be very exciting."
After England, Jones will lead a Japan XV in two games against the Maori All Blacks before the full team play home test matches against Georgia and Italy in July.
Jones named 12 uncapped players in a 35-man squad which includes 35-year-old World Cup veteran Michael Leitch.
Loose forward Kazuki Himeno, who captained Japan at last year's World Cup, will miss the summer games through injury.
"We feel the need to play in a different style, a Japanese style of play," added Jones, saying he wants his team to play with pace.
"We will be implementing that from day one. Obviously it will be difficult to learn, but we want to see the first signs of it against England."