Don't be shy! ^_^
It was quite late at night, and the two of them just finished quite an exhausting full-day mission where they had to take down an organization within twelve hours (easy, but definitely energy draining). Since the mission took place outside of Yokohama, a hotel was booked beforehand, just for one night- so here they were.
Since it was around 10 P.M., Dazai suggested that they take a shower together, just to save some time (totally just that) so that they could get some rest earlier. Chuuya was too tired to argue anyway, and that seemed like a good enough reason, so he agreed.
Well, it wasn't entirely a bad decision, but Dazai could be a bit (that's an understatement, but whatever) of a nuisance all the time- especially with Chuuya, so he was quite smug about the whole thing. "Oho~ you agreed so quickly! Does the chibikko secretly want to take a romantic shower with me?"
-That got Dazai a smack in the head. Ow! And Chuuya said he was 'tired'?! Well, what exactly was the definition of 'tired' to him, then?! Because that really did hurt. "Oww! Chuuya's a meanie." He pouted, sticking his bottom lip further out to emphasize his feigned sulk.
The bathroom itself was quite fancy, just like the rest of the hotel itself (the Port Mafia sure had the funds, of course), and the shower was quite spacious. But of course, just of course- Dazai was already planning to stand as close as possible to Chuuya.
Why, one may ask? Easy: because he wants to piss off the ginger. Why else?