Head coach Eddie Jones said England "need people who have got a samurai spirit" after naming his squad for the Rugby World Cup in Japan.
Jones gave shock call-ups to flanker Lewis Ludlam and uncapped wing Ruaridh McConnochie in the 31-man group.
Gloucester scrum-half Willi Heinz, 32, whose England debut came in Sunday's win against Wales, is also in the squad, but centre Ben Te'o is not.
"You need guys who are mature, who enjoy life," said Jones.
"And we've deliberately picked a squad like that because it's going to be an important factor.
"This is an enormous cultural event apart from being a sporting event and you've got to be able to cope with the different culture."
The World Cup runs from 20 September to 2 November, with Jones naming his squad weeks in advance of the World Rugby deadline of 8 September.
It will be the first time the tournament has been held in Asia and the England head coach believes this will make the competition even tougher.
"I think it is the most competitive World Cup," Jones told BBC Radio 5 Live Sport's Rugby Union Weekly.
"That's exacerbated by the fact it's in a neutral country and a non-rugby country which is going to add a number of distractions. The first couple of rounds some teams may struggle to adapt to the circumstances of the tournament, which is going to be different."
Another surprise inclusion in the squad was versatile back Piers Francis, who earned a place at the expense of Te'o, with the latter involved in an off-field incident at a training camp in Italy.
But Jones refused to confirm whether Te'o's exclusion from the squad was related to this event.
"I'm not going to go into the reasons why [Ben] is not selected. We've had that conversation with Ben and he understands it," he explained.
"Whether he agrees with it is another matter but we've had that discussion with him and he's just not in our top 31 players at the moment."
'It's nice to bring new blood in'
Northampton back row Ludlam, 23, impressed as he made his England debut on Sunday, but former international sevens player McConnochie, 27, was denied that opportunity, having to withdraw from the starting XV due to injury.
Although he has had limited opportunities to see them play Test rugby, Jones is certain both can contribute to England's World Cup campaign.
"It's always nice to bring new blood in," he said. "It freshens everything up and when you've got that enthusiasm as young players do, it helps to add to the squad.
"Ruaridh we've been watching quite closely through the club season. He's a good worker, good communicator. He plays a number of positions so he was an easy selection in the end.
"Lewis came from nowhere. We watched him in club rugby and he'd done particularly well. We thought we'd roll the dice, bring him into camp and see what he can offer.
"Every week he's got a little bit better. We saw against Wales a display that's only just the start of his career."
England captain Owen Farrell, 27, has been equally impressed by the new arrivals, especially those - like Ludlam, hooker Jack Singleton and Heinz - who earned their first cap in the warm-up match against Wales.
"A few of the lads who made their first cap brought a whole lot of energy and weren't waiting for anyone else to show them the way. They led from the front," Farrell said.
"The lads have done really well to get selected for the World Cup but there's still a lot of work to be done so we've got to get excited about doing that work."
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'Players left out have still got to be ready'
England's first World Cup match against Tonga on 22 September is still over a month away and Jones has already had injuries to contend with.
Tom Curry left the pitch holding his right arm early in the second half on Sunday and Jones said that would be a "small amount of weeks' injury", while the 59-year-old added Exeter wing Jack Nowell is "on track" to recover from an ankle problem in time for the World Cup.
Henry Slade and Sam Underhill were named in the starting side for the Wales game and withdrew the day before, but Jones said Slade's knee issue was a "two or three week injury" and Underhill could return before the warm-up game against Ireland on 24 August.
Nevertheless, the England head coach warned those who had been omitted from his side that they may be needed should any more serious injuries occur before the tournament begins.
He said: "They've still got to be ready because the circumstance of the World Cup dictates that you have injuries and they could get their opportunity later down the track."
England face Wales in Cardiff for their second warm-up match on 17 August, before the Test against Ireland and a final game against Italy on 6 September.
England World Cup squad
Forwards: Dan Cole (Leicester, 86 caps), Luke Cowan-Dickie (Exeter, 12), Tom Curry (Sale, 11), Ellis Genge (Leicester, 10), Jamie George (Saracens, 37), Maro Itoje (Saracens, 27), George Kruis (Saracens, 32), Joe Launchbury (Wasps, 59), Courtney Lawes (Northampton, 72), Lewis Ludlam (Northampton, 1), Joe Marler (Harlequins, 58), Kyle Sinckler (Harlequins, 22), Jack Singleton (Saracens, 1), Sam Underhill (Bath, 9), Billy Vunipola (Saracens, 42), Mako Vunipola (Saracens, 53), Mark Wilson (Newcastle/Sale, 13).
Backs: Joe Cokanasiga (Bath, 5), Elliot Daly (Saracens, 31), Owen Farrell (Saracens, 70), George Ford (Leicester Tigers, 56), Piers Francis (Northampton, 5), Willi Heinz (Gloucester, 1), Jonathan Joseph (Bath, 41), Jonny May (Leicester, 45), Ruaridh McConnochie (Bath, uncapped), Jack Nowell (Exeter, 33), Henry Slade (Exeter, 22), Manu Tuilagi (Leicester, 33), Anthony Watson (Bath, 34), Ben Youngs (Leicester, 86).