According to character designer, Daigo Ikeno, Lady's school girl outfit was inspired by 'the black-haired Julia Volkova' of the duo t.A.T.u.

"The inspiration for Lady's image is the black-haired Julia Volkova of the Russian girl group t.A.T.u. (laughs) This is a woman who sets off to kill demons all by herself, so we equipped her with weaponry that can get the job done. She had to look like a capable fighter, but... Japanese players just love school uniforms. (laughs) All the time, the members of t.A.T.u were known for their uniform-style fashion, so we designed Lady's outfit to look like a uniform too. The thing around her waist looks like a skirt at first glance, but it's actually made up of customized weaponry pouches. The hard pouches are wrapped around her waist and filled with gun magazines, but then they're decorated with a plaid pattern reminiscent of school uniforms. It's hard to say whether she custom-ordered them or made them herself. (laughs) Then there's her white button-up shirt, which feels very fresh and clean. I came up with a number of other battle-oriented designs, but in the end, the uniform look was very important. Itsuno had a big say in it, too. I may have chosen a look more suitable to fighting if it had been up to me. (laughs)"
Contributed by DrakeVagabond