Japan won\'t be short of insider knowledge when they face New Zealand on Friday with popular All Black kicking coach Mick Byrne on loan to the Brave Blossoms for the World Cup.Byrne took up the role as Japan\'s forward coach in 2009 under a deal which sees him still spend 50 days a year in the All Blacks camp and he will return to New Zealand after the World Cup final on October 23.His impact assisting Japan\'s head coach and former All Black John Kirwan was evident when the Japanese held their own against the much higher-ranked France until a 22-point burst in the last 10 minutes inflated the scoreline. All Blacks forwards coach Steve Hansen rated Byrne one of the best coaches in the world and said Tuesday he was held in high regard by both the players and coaches.\"He is a great skills coach, he understands the mechanics of coaching, the techniques of coaching. \"He comes with a lot of knowledge from us, from the New Zealand environment and he\'s put that into Japan and worked well with JK so obviously a combination that\'s working real well. \"It\'ll be a little bit like playing your brother -- you want to beat the **** out of him but you still love him.\"It\'ll be quite enjoyable, we\'ll have a few laughs. Rivalry is a good thing, especially when it\'s one of your best mates.\" Kirwan, who starred for the All Blacks during their one World Cup success in 1987, has a \"don\'t ask, don\'t tell\" agreement with Byrne on much inside knowledge is being tapped. \"I don\'t want to know. We have made that gentleman\'s agreement.\" Kirwan told reporters. \"Our game is quite unique, so we made a decision a long time ago that I wouldn\'t ask and he just has to prepare the team as best he can to play a team that he knows well. \"I feel very fortunate the All Blacks have let Mickey come and work for us and I think that\'s the beauty of our game. He\'s an outstanding coach and he has brought a lot to the table. He\'s been a big influence.\"