Official 4-koma Azur Lane: Slow Ahead! — Chapter 35-2
"Big sis St. Louis' choice of clothes are how would you put it... have a tendency to be really flashy... don't you think?" "Furthermore, she adapts the way she wears it herself..."
See Obi-spin for more on this meme.Come to think of it, it seems that there is underwear specially for use with Sakura Empire kimonos.
She's talking about the sarashi.