One effect is that it can create a huge shock for the readers. It completely changes the expected narrative direction. For example, in 'Game of Thrones', the death of Ned Stark was a turning point that made the story more unpredictable and full of high - stakes drama.
One reason could be to create a sense of shock or surprise. It makes the story more unpredictable. For example, in 'Game of Thrones', the sudden death of Ned Stark shocked readers and viewers alike, completely changing the direction of the story.
It can make readers sad. If they've become attached to a character, that character's death can be quite emotional. Like when we read about the death of Dobby in the Harry Potter series.
One pro is that it can create a huge shock value. It can jolt the readers and make them more engaged as they try to figure out how the story will progress without that character. A con could be that readers might get too attached to the character and become very disappointed or even stop reading. Another con is that it might disrupt the planned character arcs and plotlines that were centered around that character.
In Memories Off visual novels, Tsukasa Ayatsuji is a significant main character. His character development throughout the stories is interesting to follow. He interacts with other main characters like Renji Oyamada. These characters' interactions and their individual stories are what drive the overall narrative of the visual novels.
Not having read the 'killing moon novel', I can only speculate. There might be a protagonist who has a special connection to the moon, either through some sort of power or heritage. There could also be antagonists who are either causing the moon to be 'killing' or are taking advantage of the chaos it creates. And perhaps there are supporting characters like friends or mentors who help the main character on their journey to deal with the situation regarding the killing moon.
Since it's a 'killing star' novel, perhaps the main characters are those who first discover the star. They might be a team of interstellar explorers or astrophysicists. There could also be military personnel if the situation with the killing star becomes a matter of security or warfare. Maybe there's a maverick scientist who has a unique view on how to handle the situation, and a military commander who has to balance the safety of the galaxy with following protocol. These could all potentially be main characters in the story.
I don't know for sure as I haven't read this particular novel. But usually in a killing game - themed novel, there could be a strong - willed protagonist who tries to resist the game's cruel rules.