This information was greatly supplemented by Lillian D-P's script translation, available here.
The Tokyo Babylon 1999 drama is a 48:19 supplement to the movie. Contrary to what I thought when I bid for it on eBay, when Mefiant pointed it out to me, it is not a soundtrack, though it does contain the same ghetto-ass ending song used for the movie credits. It was released in 1993, the same year as the movie, and there is a number annotation on the back of the CD that reads "93*9*22, which may translate to a release date of September 22, 1993.
There are multiple subtleties and notable actions in this drama CD for both Subaru-philes and Seishirou-philes to digest. I have not mentioned all of them in the outline below. That would spoil the read, and the primary source is enough for people to formulate their own opinions and theories. It is recommended reading for fanfiction writers and fan-analysts.
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The drama takes place one month after the events of the Tokyo Babylon 1999 movie, and provides a short closure to the movie's events and the girls being placed under police surveillance. Subaru's personal assistant, Amano Heita, provides Subaru with the background of several murder cases in which the victims' bodies were entirely unmarked and have left the police wondering a supernatural element was involved. Of course, they all end up pointing to one specific person (Guess. Seriously, guess.).
Subaru must once again deal directly with the man who has become the all-encompassing core of his life in the past five years. The detailed story of a young girl's murder highlights an unearthly paradox of gentleness and absolute indifference to human life, and a momentary encounter with a woman over her husband's slain body leaves said woman enthralled with the man who ripped her life apart.
Whereas the movie focused more on Subaru than Seishirou, the drama CD focuses more on Seishirou's paradoxical, enigmatic character, providing the character development for him that was so lacking in the movie. This is Seishirou's limelight during the twilight years between Tokyo Babylon and X, and his actions and words echo of the events of five years ago in ways that baffle Subaru. When he chooses to kill, and when he allows somebody to survive; when he is kind, and when he is cruel--these are all pieces Subaru collects and nurses in his quest to figure this man out.
