For one, Yuuta's thankful for being able to use the kitchen on such short notice— one would expect him to have something for a special occasion like this one prepared in advance, but leaving cupcakes where they can be seen is the exact opposite of what he wants, isn't it? That's why he decided not to bake these at home, where his brother can walk in at the wrong time, which might lead to him helping out on his own surprise, and that would be terrible.
He knew he was capable of instinctively adding chili instead of sugar, though, so he'd needed someone to help him. He'd known who he wanted to invite from the start, but it was a bit difficult for him to approach him on it - still needing to remind himself that Tsukasa loves being with him the same way he loves being with Tsukasa - so Yuuta had stuttered and stuttered to the point where he wondered if it was still him speaking, until Tsukasa put two and together with a smile that completely betrayed his mature-sounding answer.
It's not like the two of them are absolutely useless when it comes to baking, thank goodness, that would be a disaster otherwise, but they'd needed to find a recipe to fall back on, because improvisation would have earned them pity at best— the library here had felt more like a labyrinth than anything, though, bookcases and even stairs everywhere, meaning that if he'd let go of Tsukasa's hand for even a moment he would have been be completely lost, not even knowing where to find recipe books or the door they'd taken. In fact, even now he's not even sure how Tsukasa managed to find what he was looking for without getting confused, and he knows when Tsukasa would be confused because he's one of the most expressive people he knows.
(Which is adorable.)
He had to make an excuse over the phone, though, because going to Tsukasa's house today was still unprecedented— as much as he loves his brother (which he actually can't deny now) he'd really needed him to shut up so they could find the rest of the ingredients for his gift, so he'd been a bit too aggressive, much like he was before, although he'd reassured himself it was for the greater good. After that, they'd set everything on the counter and preheated the oven, but not before Yuuta had snuck over to the spice cabinet, leaving Tsukasa to lead him back swiftly (with an iron grip on his hand, yet his hands were so soft he didn't mind in the slightest).
They'd split the next two steps among eachother, with Tsukasa in charge of the cocoa, a twinkle in his eyes when Yuuta suggested adding a little more than they needed to in the hopes that it would turn out sweeter. Even so, he of all people had rejected that suggestion, in case something would happen to the cupcakes considering they weren't even his to experiment with, so he'd immediately dropped the suggestion for both Tsukasa's and Hinata's sakes, placing his bowl of flour mixture on the side and going to watch the cocoa mixture bubble (and to watch Tsukasa marvel at the sight).
After that was said and done, and they'd mixed everything together, they'd added the rest of the ingredients, the two having alternated between mixing and adding and stealing glances at eachother (and looking away when they caught eachother staring— so Tsukasa wasn't used to this either, huh…)
It feels like hardly any time has passed overall, but all they need to do now with the cupcakes before they start on the icing is pour them in the paper cups and put them in the oven— two thirds is all they need per cup, Yuuta pouring the mixture and Tsukasa yelling "Stop!" hurriedly whenever it's time to move to the next one. Ah, he'd never get tired of his voice...
After putting the cupcakes in the oven, he notices that there's still some batter left. He'd heard that it was a bad idea to eat batter, yet his brother always does that, so considering that it would probably be a missed opportunity and wasted food, he gives it a try— had he liked sweet things, he would have more of it, meaning that it would be best to push the batter bowl towards Tsukasa, suggesting that he give it a try.
A try turns into another, and another, until he's done with the bowl and looks satisfied enough, eyes closed, cheeks a bit flushed.
Suddenly, regrettably, Yuuta feels as though he could kiss him.
He needs to get used to this now that they're a couple, he figures, even though all he can think of is how bad of an idea this is or that he really shouldn't give in to impulses so easily. A minute passes, and when Tsukasa asks if they should start the icing now he frantically stop him in his tracks.
"You... have some on your face," he remarks, much less casually than he intends to sound. Even so, Tsukasa seems to have fallen for it, wiping his face with a tissue.
"Is it gone now?"
"No, no, I'll do it!" He takes the tissue from him, only to hold it behind his back when he gives him a quick peck on the cheek.