Youmu Minase and Really Weird Cthulhu Mythos

One day, an ordinary high-school girl named Minase Youmu is kidnapped up in the mountains. Her kidnappers claim that she has taken some kind of "medicine" and that there's no going back. Luckily, though, a former detective named Sanpouji Kotetsu happens to pass by where she is being held, and rescues her. Kotetsu hastily gets the underage girl to the police, where the investigator Naru Asuka and her 'psychic' partner Hayama Reiichi take on the girl's case. Asuka, Reiichi and Kotetsu have to figure out who took Youmu--and what was done to her--before it's too late (if it isn't already)!

Source: MangaHelpers