shylily (1st costume)
The default costume of Shylily, as seen on Twitter.
She wears an orca hood with a white see-through serafuku and a blue skirt, paired with a blue halterneck bikini which she wears underneath. (There is a separate costume tag for when she's only wearing the bikini part.) She also has an alternate version of this outfit where her serafuku, skirt, and orca hood all become pink.
This tag implicates shylily (learn more).