In ch 28, Shiro kept himself from asking about skirts when he and Mephisto rode to Tokyo airport. Thanks to XxAlysxX, we know how such a questioning might have turned out.
I do not own or profit from any of what Kazue Kato has created.
At a restaurant somewhere in True Cross Town sat two men who didn't really know how they got there. Neither of them was a man either, technically, but they were in the kind of state where one tends not to care about technicalities, and certainly not how they ended up where they were. The matters that did occupy the alcohol-addled minds of these men were of far deeper importance than so.
"Hey, Mephisto-san...? I was just thinking..." No, that was a lie. And a quite bad one, too. If he had been thinking he wouldn't have opened his mouth in the first place. "Do you ever wear skirts?"
"What kind of ridiculous question is that?" Mephisto had a horrible tolerance for alcohol, but compensated for it by being smart enough not to drink as much as Shiro had. Even so, he did look a bit... fuzzy. "Who in their right mind would wear a skirt with a tailcoat?"
"Just thinking it would go well with your legs, izzall." He poured himself another cup of saké and managed to get at least most of it in the cup. "I'm drunk, aren't I? I'm thinking about a dude in a skirt." It was mildly disturbing, really.
"In vino veritas, as the Romans said", Mephisto snickered, sipping from his cup. "No, I'm more in favor of ballroom dresses. Very elegant, move gracefully when one walks, perfect for hiding one's tail~"
"Right..." He nodded to himself, a drunken smile plastering his face as images... Wait, hang on... "...tail? You have a tail?"
"I am a demon", he reminded, eyebrows rising.
Shiro's mental picture of Mephisto in True Cross Academy's female school uniform was marred by a long, arrow-tipped tail sticking out from under the skirt.
"Alright. You would look better in a ballroom dress."
"So you have worn one?"
"Why, are you very eager to see me in one? The saké unlocking some inhibited desires you won't acknowledge~?"
"Well, if you're up to it..." Shiro's lips stretched into a playful smile, scooting closer to the demon. "'Cause I really do have an inhibited desire... to yank that curl."
With dexterity that belied three-quarters of a flask of saké, Shiro grabbed the offending strand of hair and tugged.
"Ouch! Ow ow ow ow, what are you doing?!" Mephisto grabbed Shiro's wrist in one hand and his curl in the other, trying to separate the two as painlessly as possible. He almost succeeded: then he instinctively leaned backwards, away from his drunk student, forgetting that he himself wasn't entirely sober. The leaning turned into falling, and the grip on Shiro's wrist dragged him down on top of him.
"Mud-monkey!" he growled at the face that was so close their noses touched.
"You're cute when you're angry, Mephisto-pon", Shiro grinned.
"Oh, really?" His fingers snapped once, and suddenly Shiro's legs felt very cold. "You're cute when you're wearing the girls' uniform. Enjoy your walk back to the dorms." And with a second snap, he was gone.
This incident actually got its own fanart! Both of Shiro in the girls' uniform:
yfangirl1613 . deviantart gallery / 40580567# / d5kjfko
And of Mephisto in a dress:
yfangirl 1613 . deviantart gallery / 40580567# / d5kmpjd
Many thanks to YFanGirl1613~! (I still can't really believe you actually did it...)