Shukushou Byoutou

The story begins as a high school boy named Origuchi Shinobu is brought to the hospital for treatment. During his special treatment, Dr. Leona shrinks him down to the tiny size of 5cm, surely by "accident." Realizing the rare opportunity the "good" Dr. Leona now has, Origuchi becomes her personal plaything. She isn't the only to enjoy the wonders of a 5cm boy however. Your "trusted" nurse, shy classmate, and even your adorable little sister-in-law are ready to show how much they love their new favorite toy.

[from a review by Mario on DLsite English]