kiso kai ni (swimsuit mode) (kancolle)
The bikini official alternate costume of Kantai Collection's Kiso, intended to have been exclusive to her kai ni form and as seen in post #2940724. While considered an official costume, it has remained unreleased in the game apart from the 2017 calendar.
Her swimsuit consists of a black bikini with white tiger stripes, plus a brown straw hat.
This tag implicates kiso_kai_ni_(kancolle) (learn more).