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.
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 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.
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 most important character is, of course, the assassin who gets reincarnated. His skills and past experiences shape his actions 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.
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.
I'm not sure specifically as there could be many different stories with this title. But generally, it might be about an assassin who is reincarnated into a new world or a different form. Maybe they have to use their assassin skills in this new situation, like facing new enemies or challenges.
There are likely to be other important characters such as the people who train the assassin, his targets, and perhaps some allies or friends he makes along the way. However, without reading the entire light novel in detail, it's hard to name every single main character.
I'm not entirely sure without reading it, but there's likely a main assassin character. Maybe there's also a mentor figure who trained the assassin.