Kawaiiso

I told Ai I was taking the local train to Tokyo, and she replied by writing, Kawaiiso. I tried looking it up, but all I have is a phrasebook. It did have the word Kawa, which means river. I already knew the rest, "ii" (nice) "so" (so). So I thought she was calling the local train "So nice river" and I figured it was a nickname. The local train makes every stop on the way to Tokyo, so it's the slowest possible way to get there. I was all happy because I knew some cool phrase for the local train, but then later that day she said it again, and I asked her what she meant. Kawaiiso actually means "pity", she was just saying it was a pity I would be so long. Anyway, I think Kawaiiso would still be a cool nickname for the local, so I'm telling everyone to use it. It would be awesome if this Gaijin got the Japanese to use the pun.