The 19-year-old beat the Japanese wildcard 6-2, 6-2 to set up a showdown with former US Open champion Sam Stosur, who downed American teenager Madison Keys 6-1, 6-2 in the other semi at the $250,000 event on the hard courts in Osaka.
Bouchard and Nara, competing in her first WTA semi-final, traded breaks early on before the Canadian found her rhythm to reel off seven games in a row and open up a 6-2, 3-0 lead.
The fifth seed then swiftly wrapped up the win over her 21-year-old opponent, who is certain to improve her world ranking of 87 when the list is updated on Monday.
Bouchard will face a tough task to claim a first WTA title against the experienced Stosur, who is enjoying another strong showing in Osaka.
The Australian, seeded three, was a losing finalist here two years ago after she won her first career title at the event in 2009.
Her serve provided too much of a test for the promising Keys on Saturday, with the 29-year-old losing only 12 points in her eight service games.
"I thought I did everything very well today," Stosur told the WTA Tour after reaching her second final of the year.
"I always play well and enjoy my time here. And it's no trouble coming here either - at the end of the year there are a lot of tournaments in Asia, so of course I wanted to come back to this event too.
"I'm very motivated," the world number 20 said as she goes in search of her fifth career title.
"I'm really looking forward to tomorrow now. It's going to be great to be in the final again. Hopefully, I can repeat what I did four years ago instead of two years ago."
Image: Eugenie Bouchard
Photograph: Koji Watanabe/Getty Images
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