Really, Tatsujin? I watched 1 Litre of Tears, and I just couldn't really feel that horribly upset. I feel for the girl, but because I know I won't be able to go through what she did, I couldn't really connect with her as a person on an emotional level of that magnitude. At least with Clannad, Okazaki's and Nagisa's relationship is similiar in alot of ways to my own relationship with my g/f.
The connection is just hard to make with Litre than it was with Clannad. I did, however, look up the disease the girl suffered from after watching the series, and read up a bit about the girl herself. It was emotional, however I couldn't make the connection for some reason.