Complex sentence: Traumatized by the incident, Fumiya's girlfriend, Chiho, comforts Fumiya by celebrating Christmas Eve in their apartment, but he sees Chiho as the grandmother's ghost and kills her by stabbing her with a knife.
Split into simpler sentences: Traumatized by the incident, Fumiya is comforted by his girlfriend, Chiho, who celebrates Christmas Eve in their apartment. However, Fumiya sees Chiho as the grandmother's ghost and kills her by stabbing her with a knife.