Fourth season of Yatogame-chan Kansatsu Nikki.

The long war between the planet Earth and the machine men is finally over, resulting in a peace that is more a victory for the machine men than the Earth. Warrius Zero lost his family in the war to the machine men but despite this he is still is a member of the Earth fleet that is now working in concert with the machine men. His ship, made up of both humans and machine men, has been given a near impossible task: capture the space pirate Captain Harlock. While Zero struggles to accomplish this task, evidence begins to surface that the peace between machine men and Earth may not be as it seems...

In the past Mutsumi (Mucchan) and Sae (Sacchan) met. Enjoying the time together, they decided to meet again and chose a place. Mucchan, however, never came to that place. A few years later he passed through that place on his way to school, and met Sacchan, who had been waiting for him for all those years. And so, they start playing together again. However, it won't last so long, because...

A series of specials included on the Maria-sama ga Miteru DVD releases.