In the season finale, Nick's worries about a scratch Juliette received from Adalind's cat force him to reveal his Grimm heritage to her, which makes Juliette believe he has gone crazy. The latter two have their heads sent back home with a note saying to send the best next time. He kills the first in defense of Marie, and the other two are killed in self-defense after being sent Nick's lead suspect in a case. As of episode 19, Nick had successfully killed three reapers, creatures that are sent out to kill Grimms (hence the Grimm reaper title). As Nick dives deeper into his Grimm heritage, he begins to train with Monroe to learn about the wesen in Portland and to use the weapons that his aunt Marie left behind. The two tend to cross when he works cases that involve wesen, which are the creatures of the Grimm world. Throughout the first season, Nick struggles to balance his normal life and life as a Grimm.
Nick had wanted to propose to his girlfriend, Juliette, for some time, but he felt that he would have to tell her about his life as a Grimm beforehand. This power has now expressed itself as his ability to perceive the supernatural that nobody else can see.
Even before his abilities manifested, Nick had an exceptional ability to make quick and accurate deductions about individuals' motivations and pasts. Nick is a homicide detective who discovers he is descended from a line of Grimms: hunters who fight supernatural forces. Nicholas Burkhardt (played by David Giuntoli) is the show's protagonist and titular Grimm.