Have you ever thought that… Considering Pillar Men can easily manipulate their bones and muscles structure, they can change their height or size to fit in your tastes…?
I can see Wammu doing so in a way, to appear less threatening. He indeed takes a great pride in his fighting experience so he loves to unintentionally boast with his figure that easily overpower any bodybuilder, but he wouldn't see a problem to get a bit shorter so your neck wouldn't hurt when you talk with him.
However, if you ask him to grow bigger, he's a bit confused, as the way he already can see the crown of your head is a clear sight that you two are already on different height levels. Why do you want even more drastic contrast? When it comes to you, Wammu is a bit nervous, afraid of hurting you with hands that were used mostly to kill, not to caress... Reminding himself that one of the main traits of a great warrior is controlling the strength of his touch, he would do his best to not squeeze your waist too much when his enlarged hands would envelop it easily.
However, someone like Kars is too derisive for such a compromise. The pride he took in his appearance is higher than Wammu’s, at least insofar as his grace was also considered, and not only sheer body power. The height and size difference between you two would be the main reason for his teasing flirt and remarks. He would also use it to set the rules from the start, as his towering position would totally be a reflection of how he overpower you in mentally aspect too, being the one who's controlling the relationship.
So no success in making him shorter, yet… Although he isn't really into the whole size difference kink, he would enjoy getting bigger if it is what you ask for. To make you feel helpless one grasp of his hand should be enough, but if you want the contrast to be so demonstrative, then be it, it actually feeds Kars’s confidence in a strange way.
