"Sluttiest character" is kinda a meaningless title imho, here, I shall construct the sluttiest character to ever exist:
Nymphora, goddess of Sex, Beauty, and Debauchery, snapped her fingers and created an uncountably infinite number of universes with an uncountably infinite number of creatures in each, then created an uncountably infinite number of copies of herself so she could simultaneously have sex with everything in every universe at once.
(You could, in theory, always construct a sluttier character than Nymphora, by creating another character who does the same thing except taking the power set of the number of partners they have to construct a greater infinity. By Cantor's paradox, it's impossible to construct a cardinality so large that it's not possible to construct a greater cardinality out of it. But this character would not be sluttier in an *interesting* way, and so we shall discard the possibility from consideration.)