Seras is a vampire, so don't expect to be able to take her by force easily, if at all. Fortunately, she enjoys a good binding as a means of unwinding to take care to befriend her. No matter what she's wearing, any tie and material should emphasize her chest as it is both her best feature and weak spot. Feel free to CCR her into an outfit and emphasizes it even more for that much more fun. Give her a ballgag or a bitgag so she's able to bite down on something but feel free to add some cloths or tape over that to emphasize her sharp, piercing eyes.