The Manchester United midfielder feels that the Samurai Blue fell well below supporters' "strong expectations" after finishing bottom of Group C at the World Cup
The Samurai Blue were beaten 4-1 by Colombia on Tuesday to send them home from Brazil with only a single point.
Kagawa himself played only 204 minutes, substituted in both of his starts and brought off the bench in their second game, a 0-0 draw with Greece, and is frustrated with his own performances in a competition where promising things had been expected of his national side.
"I know many fans were rooting for us and I felt their strong expectations," he told reporters after the defeat.
"But I just wasn't good enough to achieve anything and I feel sorry for letting them down. It is frustrating that the World Cup is now over.
"My career goes on," he replied when asked about what came next for him, with talk of a departure from Old Trafford continuing after two difficult seasons at United.
"It might take some time to accept this but I’ll prepare myself to move on."