Doctor Who

A mad idiot in a box, traveling through time and space, stopping by to help.

This is Doctor Who about an alien who tries to help by fighting evil and aiding people. The Doctor, the alien, has the power to regenerate into multiple incarnations which allow plenty of options for stories. As does his many many companions (mostly female) and enemies.

But what happens when those adventures become erotic? Sexual?

These stories are what happens. So pick a character. A Doctor, a Companion, an Enemy even... Then tell the story.