The Rays acquired Allen off waivers from Oakland on April 19. He batted .154 with one home run and three RBIs during his seven-game stint with the Rays. He was hitting .262 with four home runs and 14 RBIs with Triple-A Durham.
"I liked the guy," Rays manager Joe Maddon said. "Would I like to keep him? Absolutely. What's the fairest thing? What just happened."
Maddon said he was happy for Allen.
"He's a great guy and I'd like to see him just tear it up over there," said Maddon, who explained that a player being sold to a Japanese team must first give his permission. "And you can't blame him. I'm sure the money's going to be better than he would be able to get here. He's got to look out for his family. I think it's a good move for him."