Who do te think Train really 'is'? The serious person o the one who always laughs (lazy)? Why?

I think when he was black cat, he has to behave himself like an adult but when he became a sweeper he can be himself. But sometimes he has to be serious when he is mad o because he has to concentrate himself. (-o-)i

a bit of both depending on the situation

It's both. If it's a serious situation, then he's serious, but many times, he's just lazy.