The man, now 21, was involved in the attempted hijack of the 106,000-dwt Guanabara (built 2007) in March 2011, off the coast of Oman.
Three other men have already been convicted of the attack.
The hijacking was foiled when US navy personnel captured the pirates and turned them over to the Japan Coast Guard.
Two of the four pleaded guilty and received 10-year prison terms.
The
