Wait, Berlin to Brussels for €9? Good lord, that is far too cheap. For example, the distance is roughly equivalent to Denver-Albuquerque. Kayak's cheapest quote is $119 one way, scheduled 1 month in advance. I knew flights in Europe were cheaper, but how is it possible to operate profitably at that price? Kayak shows $23 for Ryanair Berlin-Brussels.
For comparison, I had a vehicle breakdown and needed to take an (awful) bus that distance in the US, and it cost far more than $23 (IIRC, it was ~$75 and took 18 hours).