ももえろ濃霧注意報!

Taichi and Nazuna, his younger sister, have transferred to a new school. On their first day at school, a rumour spreads that Taichi slept with Nazuna because of her brother complex. A strange girl named Yuiri also appears in front of them who just set up the Edo Customs Research Club. Taichi is forced to join it.... He meets other club members, Saki, Suzuka, Kazuha, Shouta, and Ruka there and lives an eventful school life. One day, a mysterious mist that arouses sexual desire suddenly surrounds the school. When it happens Taichi and Yuiri are together.

"Stop it! Don't look at me!"
"Well, you are looking at me with erotic eyes."
"Don't say that! I'll never...."
"Oh, it's no good...."

They finally sleep together.

On the next day, Yuiri and other club members decide to examine how the mist appeared. But one day, another mysterious phenomenon happens and Taichi is forgotten by his friends...