Billy Vunipola has revealed how crucial his relationship is with his brother and England team-mate Mako, ahead of Saturday's game against Argentina.
Eddie Jones' men face the Pumas after big wins over Tonga and the USA, with their final Rugby World Cup Pool C match coming against France on October 12 before the knockout stage commences.
What could be key to England's success is the relationship between Billy Vunipola, who has started the last six games, and his brother Mako, who is expected to be available to face Argentina after coming through training on Friday.
Mako, who has played only 17 minutes in four-and-a-half months since injuring his hamstring for Saracens on May 11, is competing with Joe Marler and Ellis Genge for a starting berth at loosehead prop in Tokyo.
"I think me and my brother have a certain level of trust that will always be above and beyond anything I have with anyone else," Billy Vunipola told Sky Sports.
"I know what he can do and I can always ask him for more - I can tell him [things] too. He knows what I do, his biggest job with me is probably cooling me down, because a lot of my game is based on emotion.
"That relationship, being brothers, is totally different to anything else that we have as a group. We have each other's backs, he loves me.
"If he says something and it comes across a bit strong, I know it is coming from a good place, you don't always get that with everyone - maybe a best friend. But it's rare, and that's the difference.
"I think with his recent experiences of being injured, having a positive mindset will help him more than hinder him. He thinks that being positive sometimes is fake, but sometimes you've got to fake it until you make it!"
Marler has played as Jones' senior loosehead in the absence of Mako Vunipola but is aware his spot in the starting line-up is under threat again.
"There are three guys going for two shirts, so that doesn't work. It's great to have Mako back and he's been in training for the last couple of weeks anyway," Marler said.
"He's back fully fit and he brings world-class experience and talent into that role. So...I've enjoyed my time!
"I'm determined to give as much as I can to this group to help us win the game on Saturday."
'Sorry Eddie, I ate a lot of Kobe beef!'
Billy Vunipola also reeled off some amusing anecdotes from his time in Japan, revealing how he accidentally held up traffic on a toll road for electric cars, explored Osaka, watched rugby and "ate a lot of Kobe beef".
When asked how he had spent the last few days off, he said: "Probably exactly the way Eddie didn't want me to do - I ate a lot of Kobe beef!
"I just wanted to sample it a little bit more, it was a different cut. It's not as good as Miyazaki. We cooked our own and it was better.
"I also went for a walk with my wife. She loves walking, so we walked around Osaka. It was really busy, we struggled to find parking and I couldn't understand anything!
"I went on the electrical [car] toll road by accident and held up traffic! I didn't have enough money on me, there was no card machine, so I was let off.
"I spent half my time watching rugby. We were in Osaka so we went into a pub and watched Tonga vs Argentina and Japan vs Ireland. I got to do the things I wanted to do - and I didn't eat too much!"