so a college student and a detective shoot a gun at each other and the bullets hit each other and they switch bodies. Later you find out that the detective is a serial killer with a modified body and the killer is using this new body that he has to kill more people. Details include a little girl staying with the protagonist after the body switch and another killer staying with him. Also hes looking for a mastermind of the modified body project that the original detective went through and this person also plants bombs

Change the World (KANZAKI Yuuya)

yup thanks