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Akiyoshi, who was one-under for the tournament, finished ahead of New Zealand's Michael Hendry and the Japanese pair of Masahiro Kawamura and Masanori Kobayashi who were in a three-way tie for second place.
The second-placed trio, who finished one stroke behind Akiyoshi, also qualified for the 147th Open at Carnoustie in Scotland from July 19-22.
Akiyoshi negotiated windy conditions to prevail at the Royal Golf Club in Ibaraki on Sunday.
The 27-year-old carded five birdies and three bogeys in the final round to secure his first title on the Japan Golf Tour.
Overnight leader Hendry endured a rocky finish but did enough to ensure a top-four spot and make the grade for the Open for the second straight year via this tournament.