Carter is reported to have agreed a two-year deal with the Steelers and in an interview with Canal Plus announced he would move on.
“It’s been a very tough decision, to leave my new friends and all my team-mates and go play for Kobe Steelers,” said the World Cup winner.
“But Japan is a very exciting place to be right now, and an exciting place to play.
“It’s also only one flight away from New Zealand and the way the Japanese season is structured means I and my family will be able to spend much more time in New Zealand.
“Rugby is going crazy in Japan and this is a very exciting challenge.”
He added: “Now that my mind is made up I’m determined to get over this knee injury because we want to win the Top 14 and we want to win in Europe too.
“I hope to be playing again soon.”