And finally the reason behind the name of the series has been revealed. "Seifuku", Uniform.
If it had been the English word Uniform, it could've been a pun of Yuunagi's name.
The "Yuu" sounds a bit similar to the "U" in Uniform, especially when spoken with a Japanese dialect.
Damn. Sad there’s only a few chapters left. You can see where Matsumoto-san had ideas of where to go with this manga, but I’m pretty sad we won’t be see much more. Thank you for all the Yuu/Nana goodness though. Hopefully we get more disgustingly sweet gooey romance for the last chapters lmao.