[chryuop]

How about you write it in English and then rewrite it in Japanese? That's how I do it with my pen pal in Japan.
This way you avoid problems. I wrote something to my pen pal in Japanese that turned out pretty offensive (thank you MMM, I finally understood why it was wrong), but thanks to the text in English he understood what I wanted to say.
Same thing for me. Sometimes I don't understand something out of his English because uses the wrong verb or tense, but since I read first the text in Japanese it all makes sense in the end.
This way you can keep your English more truthful and so will be the Japanese text.

You are both trying to learn, so help one another the best you can.