The New Zealand born player was sent off in the 47-5 Pool A win over the Samoans in Fukuoka on Saturday, for a high tackle on UJ Seuteni.
Aki faced a disciplinary hearing in Tokyo on Monday night, contesting the red card decision in a bid to be available for Saturday's World Cup quarter-final against New Zealand.
But the 29-year-old failed in that quest and was hit with a three-week ban, that would even rule him out of the World Cup final, should Ireland make it that far.