A: No, it's completely optional. It does not advance the main story. Watch it if you want more time with the characters, especially Nana. If you skip it, you miss nothing crucial for understanding episodes 11-13.
Each episode runs approximately 24 minutes (standard for most anime). Episode 1 runs slightly longer (approx. 26 minutes) due to the extended prologue.
So, to answer the original query definitively:
The series is known for its dual-language titles (German and Japanese), reflecting its dark, philosophical themes. English Title Japanese Title Original Air Date A Chance Encounter July 25, 2004 Annihilation August 1, 2004 Deep Feelings August 8, 2004 Attack August 15, 2004 August 22, 2004 Innermost Feelings August 29, 2004 Confrontation September 5, 2004 The Beginning September 12, 2004 Reminiscence September 19, 2004 Infant September 26, 2004 Complication October 3, 2004 Quagmire October 10, 2004 No Return Erleuchtung October 17, 2004 In the Rain... (Ep 10.5)