Rudeus is definitely one of the most memorable. His journey from a loser in his past life to a capable and respected person in the new world is very engaging. Eris is also quite memorable. Her fiery personality and her relationship with Rudeus, from being his student to something more, is interesting.
There's Sylphiette. She is one of Rudeus' friends and later love interests. She has her own growth arc and her relationship with Rudeus is a key part of the story. Eris Boreas Greyrat is another important character. She is a noble and has a feisty personality. Her interactions with Rudeus are full of energy and she also plays a role in his development.
In Mushoku Tensei light novels, the main character that stands out is Rudeus Greyrat. He's a character full of contradictions. He has the intelligence and knowledge from his past life but still has to learn a great deal about emotions and relationships in the new world. Eris Boreas Greyrat is a key female character. She is feisty and her interactions with Rudeus, from initial animosity to a deeper connection, are a big part of the story. Additionally, Sylphiette is also an important character, with her own story arc and relationship with Rudeus that adds to the overall richness of the narrative.
There is also Eris Boreas Greyrat. She has a complex relationship with the protagonist and plays an important role in his development and the overall story.
Rudeus Greyrat is one of the main characters. He is the reincarnated protagonist. Sylphiette is also important, being one of his friends and later love interests. Paul Greyrat, Rudeus' father, is another key character who has a big influence on Rudeus' early life.
Hitogami is a very interesting and memorable character. He has his own motives and plans, and his interactions with Rudeus add a lot of mystery and intrigue to the story. There's also Ruijerd Superdia. His loyalty and his own backstory as a member of the Demon Race make him a unique and memorable part of the Mushoku Tensei Novel.
Hard to say. It could be on hiatus, but without concrete information, it's difficult to give a definite answer. Try following the mangaka's social media or the manga's official website for the latest.