GNM - Hateshinai Rasen

From MangaHelpers:

College student Kazuki had a serious heart condition, and his only hope was a heart transplant. Luckily, his father was a highly regarded doctor, and he was determined to do whatever it took to save his son. After his surgery, Kazuki seemed to have recovered completely, but he was surprised to see that he had no visible scar. Mysteriously, his father also suddenly became unable to meet with him. After his girlfriend Ami got bit by some strange, giant 'bug', she encountered a violent, fully-grown clone of herself. Could this bug and the clone have something to do with Kazuki's recovery and with a string of recent murders in the area? [tethysdust]