Kou is the only one of the original Dairangers who doesn't reappear for the "Where Are They Now?" Epilogue, leading some fans to speculate that he could have turned to clay like Shadam. However, Lin has a photo of a middle-aged Kou and it's implied they were married, suggesting that he lived for some time after the main events of the show.
These speculations more than likely came from fans who didn't speak Japanese watching the raws and guessing at what the characters were saying. Lin's dialog during the pan over the photos in question explains that Kou couldn't attend the Dairanger's reunion due to a business meeting.
Master Kaku reveals in the final episode that the You and Chi powers both sides use are two sides of the same coin, destined to fight in a never-ending battle for survival. And since Kaku's attempt take the Gohma throne and stop the war failed, the only hope for the world now is the inevitable return of Daijinryū. No wonder why older!Ryo looks terrified as he watches his grandson transform....
Not to mention that Shadam's turning into clay in the final battle has you wondering if some bigger force has wanted to force Daijinryū's hand all along.