Maybe a young woman who lives in a house and the male ghost next door. The woman could be curious about the strange happenings in the neighboring house which are caused by the ghost, and that could be the start of their relationship.
It could be a lonely man who discovers that his new neighbor is a ghost. As he gets to know the ghost more, they start to fall in love. Another possibility is that it could be two ghosts from different time periods who meet in the present day and fall in love while living in neighboring 'ghostly' spaces.
The main characters might be a young couple where one of them dies suddenly and becomes a ghost. But their love is so strong that the living one can still sense the ghost's presence next door. It could be about how they continue their relationship in this new, rather spooky situation. It could also show how love doesn't end with death and how they try to overcome the barriers between the living and the dead world.
The main characters could be the spies themselves. They are probably highly trained individuals with different skills and personalities. There may be a lead spy who is in charge of the 'Operation Ghost Stories'. Additionally, there could be local characters in the neighborhood who interact with the spies. For instance, a curious neighbor who stumbles upon the spies' activities and becomes either an ally or a hindrance. Maybe there are also some villains in the story who are the targets of the spies' operation and are somehow related to the 'ghost stories', perhaps using the idea of ghosts to cover up their own illegal or dangerous activities.
Obviously, the boy next door is one of the main characters. There might also be the narrator, who could be a neighbor or someone who has a close relationship with the boy next door.
As I don't know the story, it could be the parents in the family next door, their children, or maybe even the family pet.
Since I don't know the specific story, it could be the star, who is likely a central character. And probably the neighbor who discovers or has a relationship with the star.
I don't know as the information given is too limited. But it's likely that the girl next door is a main character, and perhaps there are also her family members, friends, or neighbors.
There could be a neighbor as another main character. Maybe an older person who gives the girl advice, or a peer who becomes her friend or rival. For example, if it's a story about the girl's musical journey, the neighbor could be a retired musician who mentors her.
The main characters would be the widowed cougar, who is likely a confident, independent woman in her 40s or 50s. And the neighbor, who could be a younger man, maybe in his 20s or 30s, who is either single or just out of a relationship.
Another option is to have Hinata and Numbuh Three as the main characters. Hinata's shyness and her growth in Naruto could be paralleled with Numbuh Three's own journey of self - discovery in the KND. They could support each other and show different aspects of courage in the face of challenges.
Love, obviously. It's in the title. The love between a human and a ghost.
I'm not sure as not much is given. But probably the main character is the 'devil' neighbor and perhaps some of the neighbors who were affected by this person.