Kagawa, 25, may have been playing for Japan since 2008, but he was not selected in Takeshi Okada's 23-man squad for the last World Cup in South Africa in 2010. However, shortly after the tournament, he signed on for German side Borussia Dortmund, and has become a key member of the national team ever since.
His spell with Dortmund was simply stunning; 29 goals in two seasons from midfield saw him become one of the hottest properties in European football, and it was ho surprise that he eventually left Signal Iduna Park to sign for Manchester United in a £17m deal.
Despite the high hopes for Kagawa upon his arrival at Old Trafford, his time there has been marred by fitness concerns, inconsistency and being played out of position - giving him just six goals in two seasons, a far cry from the form he showed with Dortmund.
Having been consistently linked with a move away from United in recent months, Kagawa is entering a key stage of his career. Set to play in his first World Cup, Kagawa - who notoriously plays better for Japan than he does for United - needs to impress new boss Louis van Gaal in order to prove that he should have a future at United.
If he can turn in positive displays for Alberto Zaccheroni's Japan, then it could give him the boost he needs to kick on and make himself a success at Old Trafford. However, if he shows similar form to that of his two years with the Red Devils, then it could be the end of the road for the playmaker at United.
It's a pivotal tournament for Kagawa. Japan could very well get out of Group C, but they need their star players to perform in order to do so - and that means relying heavily on Kagawa. Whether he will sink or swim remains to be seen, but this World Cup could shape the immediate future for the midfielder.