Nico Robin (post time skip) and Rebecca (One piece) sharing a double dildo. Both are dressed in sexy cat girl outfits.
Stockings/thigh high boots on one or both characters. Nothing with too much fur, mainly just the ears and a few other small add ons.
Reina from Queen's Blade x Rebecca from OP like this (Image ) and Saber (F/S) x Erza (armor of seduction) from FT like this (Image ) in the Dressrosa Colloseum Arena. Artist to decide which ones are strapped..