Tanjiro, Inosuke, Zenitsu: In the water splashing each other

Shinobu, Mitsuri, Nezuko, Kanao, Aoi: Playing volleyball

Sanemi, Obanai, Giyuu, Muichiro: shooting each other with water guns

Rengoku and Uzui: Watching everyone doing their own things

You were sun bathing drink soda just relaxing (You can change what you are doing if you want)