Upotte!! Things

Bikinis are typically two-piece swimsuits for women, available in many different styles and colors. It's like waterproof underwear.

Gym Uniforms are usually worn by students during Gym Class/P.E. and sometimes as cosplay. Typical gym uniforms consist of white t-shirts and bloomers for girls and shorts for boys.

The character is wearing school uniform. Most probably he/she's a student.

A Swimsuit is a one-piece article of clothing that is designed for participating in different manners of water based events. Worn casually by the more modest.