I did not watch the first season of Ashita no Jo, as I was not able to find it through my usual means of accessing Anime. After having watched Ashita no Jo 2, I can confidently say that you do not need to watch the first season to enjoy the second. It does reference the first season a number of times, but in such a way that it fills the blanks while doing so.
Ashita no Jo 2 is a special anime. The show does not try to convince you to have a certain perspective about the protaganist and his flaws, it simply takes you on a journey where some of the most powerful and inspiring aspects of human nature can also represent the most heart-breaking and disappointing results.
AJ2 seemed like it was going to be one thing as I ventured into the first half of the show, but it became something that held more depth, pain and within those qualities, beauty - than I imagined it would.
I believe that we as viewers are most drawn to characters in movies/books/tv that convincingly represent human traits and flaws in their more extreme places on the spectrum. Jo Yabuki is the epitome of finding fulfilment in the simplicity of one's passion, at cost to all other things, if necessary. The people around him represent balanced desire, normalcy, without this being portrayed as negative. He is what many wish to be, but fear being. Passion, in it's purest, most undiluted form. How beautiful, how tragic.