[Ogo]

RPGs are somewhat unique in that they emphasize the group of adventuring heroes. This pattern can be found in lots of stories, of course (Lord of the Rings, super teams in comics, military stories) but the general narrative pattern in all of fiction is the single hero: a gumshoe, a martial artist, a vampire, a super-hero, what-have-you.

When designing scenarios for the group-of-heroes, you can be sort of "character agnostic", that is, you can think up challenges that are interesting or difficult in-and-of-themselves, and let the group collectively figure out how to solve them, giving each character a moment in the spotlight, (or helping each other suffer through failure)

With a single character you really have to design the scenarios with that character in mind. You end up, in effect, having to play exactly to that character's strengths, and only occasionally pressing against his/her weaknesses. So, it would help to work with the player during character design.

Think of it like this: nobody wants to see Columbo getting the crap kicked out of him by a bunch of pajama-wearing mooks, and nobody wants to see Bruce Lee figure out who poisoned the gardener at the country club! The same principle applies here; there's only two of you playing, so it ought to be interesting and enjoyable, not a high-lethality grind.

Whatever the character is should determine the kind of trouble he/she gets into.