As I've mentioned in the past, my wife is a big fan of anal sex. I once tried to buy her a butt plug online; I selected "medium" as she was already experience with anal penetration, but to our horror, the beast that arrived measured a good 4cm or so across at the widest point - far too large! It's seen some use as a dildo instead, but the shape's really not right for that.
However, for Valentine's day, I bought her a new one, along with a bulk pack of one hundred and forty four condoms. She's recovering from surgery at the moment, and her pelvis is quite painful due to her not getting enough exercise thanks to the recovery, so we couldn't really have sex at the time - her presents were things for her to look forward to as she recovered! This plug was chosen much more carefully; I found out its dimensions, and got one made of nice soft silicone rubber.
Anyway, it was a while before she felt strong enough to try out sex again. She didn't want to dive into the butt plug straight away, so when she felt ready to try having sex again, I just fucked her cunt, nice and simple, missionary style. However, we snuggled for quite some time afterwards, and I started getting hard again; with the first time having gone OK, she decided to try the plug. We put a towel under her in case lube got on the sheets, then she lifted her legs up against her chest to give me easy access. I covered the plug in KY and pushed the tip in; gently, I worked it all the way in, to her delight.
But the best bit was when I then shoved my hard cock into her cunt and fucked her. I could feel the plug - not as a distinct shape so much as a tighter pressure within her on the base of my cock. But it felt great for her, like being fucked in both holes at once. We fucked enthusiastically until I came, and she made a lot of noise!
Next time we try the plug out, I'm going to replace it with my cock after a bit of cunt-fucking, I think!