Everyone say hello to Jean, just your average schmuck of a rat trying to get by in a world that seems determined to rain on his parade. One major way in which the world has seen fit to make Jean's life more difficult is that he actually has an extreme genetic predisposition to being transformed.

Anything with even the slightest transformative effect will affect him, be it chemical, magical or miscellaneous in nature. What's more, he will react much more strongly to any transformative effects than a normal person.

This instability means he's also easier to turn back to normal, and his mind is actually quite resistant to alteration, but that just means he's fully aware of how messed up he might have become once transformed.

Poor guy.