The resulting company will be called Tecmo Koei Holdings, which will form in April.
The report added that Tecmo's second-largest shareholder, Effissimo Capital Management could sell its 18 percent stake. The company was against the merger.
Tecmo had been an acquisition target last year when Square-Enix made a move for the Dead or Alive and Ninja Gaiden publisher. But Tecmo rejected the offer and was soon in serious negotiations with Koei, best known for the Dynasty Warriors (pictured) series.
Under the deal Koei will take over Tecmo in a stock agreement worth 20 billion yen.