先生、膣内に触手を挿入れて！～学費をカラダで支払う女子校生・未枝～

Mie is promising student in a certain all-girl school. She somehow under financial difficulties and unable to sustain the school fees. One day, her homeroom teacher went on a leave for some reasons. Noriaki took over his place as substitute teacher. His true identity, however, is a space alien who breeds and sells tentacles for sexual pet.

On the very first day of his duty, he offered Mei more than just full financial support. In exchange, she must become the test subject for his 'merchandise'. Reluctant, but after some persuasions, she accepted the offer... And so, she must get involve with various experiments involving tentacles.