Mago no Kyokon no Toriko ni Narimashita ~Kazoku Ryokou de, Obaa-chan ga Fudeoroshi~

Tae, her daughter, her son-in-law, and her grandson visit a traditional onsen to celebrate her 60th birthday. Tae's grandson mistakenly bathes in the open-air bath during the women's bathing hour, quickly realizes his mistake when a group of women enter, and ducks behind a large rock to hide. Behind the rock, however, he finds himself up-close-and-personal with his naked grandmother...