Palpatine/Obi-Wan. Anything, if it is IC, consensual (or dubious consensual) and Obi-Wan is on Light side of the Force.

+ bonus if Obi-Wan knows that Palpatine is Darth Sidius
+ bonus if they understand each other and bond over sharing an apprentice, although they still can strongly disapprove each other
+ bonus if you make it Obi-Wan/Anakin\Palpatine
+ bonus for double penetration