It's possible that there are also some friends or allies that the assassin makes along the way. These could be other adventurers or people with special abilities. They might join forces with the assassin for various reasons, like a common goal or mutual benefit.
There may be characters who oppose the reincarnated assassin. Maybe there are powerful nobles or other assassins in this new world who see him as a threat. Their interactions and power struggles could be a major part of the story.
The main character is, of course, the world's greatest assassin who gets reincarnated. But without having read the entire novel in detail, it's hard to say exactly who else might be important. There could be a mentor figure in the new world who helps him adapt.
The central character is the reincarnated assassin. He is likely to be surrounded by various characters. There might be a female lead who he forms a bond with, either as a friend or something more. There could also be characters from his past life who somehow have a connection to his new existence, like an old rival who has also been reincarnated or an old master whose teachings still influence him in the new world.
There's also the people he meets in his new life. There's a girl who becomes his ally. She has some special abilities and she helps him understand the new world better. And there are some antagonists too. They are often those in power or with some dark motives who try to stop the main character from achieving his goals.
The main character, the reincarnated assassin, is the focal point. However, there may be a group of allies. For example, a group of adventurers who team up with the assassin. Each of these adventurers may have their own unique skills and personalities. There could also be a wise old wizard - type character who provides knowledge and guidance to the assassin throughout their journey in the new world.
In this novel, the reincarnated assassin is the central character. Alongside, there could be characters who are part of the new world order. For example, there might be a powerful noble who has an impact on the assassin's new life. There may also be other assassins or fighters who cross paths with the main character and either become friends or foes depending on the situation.
Since I don't know the exact 'best assassin reincarnated light novel', it's hard to say. But usually, there would be the assassin who is reincarnated as the main character. There might also be some characters who become their allies, like a magic user who helps them understand the new world they are in, or an old acquaintance from their past life who also gets reincarnated.
The main character, the reincarnated assassin, is at the center of the story. Alongside them, there could be a love interest. This character might be someone who initially doesn't understand the assassin's ways but gradually comes to accept and even admire them. There may also be a group of side characters who are part of a guild or organization that the assassin gets involved with, each with their own backstories and motives.
One reason is its unique concept. The idea of the world's greatest assassin being reincarnated into a different world brings a fresh take on the isekai genre. It allows for interesting character development as the assassin has to adapt to a new environment with different rules and powers.
The most important character is, of course, the assassin who gets reincarnated. His skills and past experiences shape his actions in the new world.
Another theme might be power and its consequences. As an assassin, he has a certain kind of power. The novel could explore how this power affects him and those around him. For instance, does it isolate him or attract unwanted attention?
The world - building in this light novel also plays an important role. It could be a fantasy world with unique magic systems or a more historical - like setting. The settings would affect the assassin's actions and the overall atmosphere of the story. If it's a fantasy world, there might be magical creatures and spells that the assassin has to deal with.