What I can remember from this anime is a little fat guy in a suit who turned out to be the devil. Main character was boy. I think the fat guy was showing him different realities. At the end he finds out that his reality is on the back of a flying turtle in space. There was a love interest with a girl (possibly an alien girl). One scene the fat guy gave the boy a herm of women but he wanted to be with the girl instead.

Sounds like,.

Urusei Yatsura
Beautiful Dreamer