"Onii-chan, I can't hold it in anymore... because I love you!"

The passionate love story between a little sister and the older brother she looks up to!
The protagonist, the older brother Hoshino Tatsuya, and the younger sister Akari, have always lived just by the two of them.
Because their mother passed away when they were really young, Akari took it as her mission to become the mother of the household instead.
Due to this, Tatsuya developed into a siscon, which he is aware of. Akari was also a brocon, and every day was no different from the other, with the siblings sharing some physical contact between siblings.

Despite his life being heavenly, Tatsuya woke up and realized that he needs to do something with his life. So he started living on his own, studying hard to become a teacher. Akari started developing into a more girly girl while he was gone.

Couple years have gone by. And so the new spring semester came, with the new freshmen rolling into the high school. Tatsuya were also to become one of the freshmen's class' homeroom teacher.
On the first day, he was surprised when he went to greet in his new class for the first time... his younger sister, Akari, happened to be one of his class' students.

[Edited from Getchu]