Avenging Spirit

The story begins when the main character and his girlfriend are on a date when a group of strangers ambushes, they kidnap the protagonist’s girlfriend and kill him. After becoming a ghost, the protagonist meets his girlfriend’s father and learns that he is a scientist who studies ghosts. He asked him to rescue his daughter and promised that he would find a way to free him. As the main character is also a ghost, you can invade any enemy you may encounter and use their own strength to fight other people including dangerous bosses.