Lupica, another one of the legion of space princesses that all seem to have found out about Earth in some tour book, appears and abducts Ataru! 

But Lupica isn't after Ataru for his great looks or charming personality (because he doesn't have either). Lupica's goal is the greatest love potion in the galaxy, which she intends to use to induce her sweetheart to tie the knot. To get it, she needs the possessor of the greatest lust in the universe...

(Source: AniDB)

The peaceful days turn out to be short-lived as the shadow of another Selector Battle looms large. Kiyoi Mizushima is the first to notice that things are amiss, and she makes her move to put an end to the cycle of darkness.The Battle this time includes a new card, "Key," and has been set up with rules different than before. With both the mastermind and their motive shrouded in mystery, the darkness grows ever deeper and more menacing. Suzuko Homura, Chinatsu Morishita, Hanna Mikage, Ruuko Kominato, Yuzuki Kurebayashi, Hitoe Uemura, and Akira Aoi, the Selectors gather once again. (Source: ANN)

Thirteenth episode delivered as a bonus Blu-ray disc to customers who pre-order all six Blu-ray volumes.

Tetsurou Hoshino is a boy bent on obtaining an immortal mechanical body in order to take revenge against his mother's murderer, the machine man Count Mecha. However, due to the incredible cost of obtaining what he seeks, his only hope is to steal a boarding pass for the Galaxy Express 999, a space train that travels across the galaxy and whose final stop is a planet where the metal replacements are provided for free. After swiping a pass, Tetsurou is pursued by the police and ends up collapsing into the arms of a mysterious woman named Maetel, who closely resembles his mother. Once he awakens, she tells the boy that she will provide him entry onto the 999 as long as he agrees to travel with her. Accepting her proposition, Tetsurou boards the cosmic railway with Maetel and begins a journey across the galaxy.

[Written by MAL Rewrite]