There might be some human characters that stand out too. A kind - hearted child who befriends the dog without any prejudice. Or an old hermit who seems to understand the dog's special situation and has some secrets related to the reincarnation concept in the novel.
The dog protagonist itself is surely interesting. It has the mind of a human trapped in a dog's body, which creates a lot of comical and also thought - provoking situations.
The reincarnated aristocrat themselves is an interesting character. Their knowledge from their past life combined with the new challenges in the aristocratic world makes them unique. Then there might be a wise old butler or advisor, who provides guidance and insights to the main character.
The protagonist, of course. As a reincarnated goblin, their journey and growth are central to the story. There might also be a wise elder goblin who imparts knowledge and wisdom to the protagonist. And perhaps a rival goblin who challenges the protagonist's status within the tribe.
There's likely the main character who is the reincarnated dragon. Their unique perspective as a human turned dragon is quite interesting. And there may be other dragons that they interact with, some might be friendly and some hostile. Also, characters from other races like wise old elves or strong dwarven warriors could be part of the story.
The cat protagonist is surely one of the most interesting characters. Since it has the mind of a human, its reactions to the world as a cat are unique. Maybe there are also some other animals like a wise old owl or a friendly dog that make the story more interesting with their different personalities and behaviors.
Shion is an interesting character. She's a strong ogre who is extremely loyal to Rimuru. Her clumsy yet endearing nature, especially when it comes to cooking, adds a touch of humor to the story. Then there's Benimaru. He's a very capable leader among the ogres. His respect and admiration for Rimuru, and his own skills in combat and strategy, make him a great addition to the cast.
The dragon itself is an interesting character as it has to navigate its new life as a dragon. There might also be other dragons that it meets, each with their own personalities and motives. And perhaps some friendly or not - so - friendly creatures that cross its path during its adventures.
Well, I think friendship could also be a theme. The dog might form bonds with other animals or even some humans, which would be a new kind of relationship compared to when they were human. Also, there could be a theme of self - discovery. The character has to figure out who they are now as a dog and what their purpose is in this new life.
Since it's a light novel about being reincarnated as a hot spring, there could be characters who discover the hot spring. Maybe there's a curious adventurer who becomes a regular visitor and forms a bond with the hot spring in a unique way. He or she might talk to the hot spring as if it has a personality.
The protagonist is usually quite interesting as they adapt to the new RPG world. They bring their own modern - world knowledge into this strange new place. Also, the mentor - like characters can be really engaging. They guide the protagonist and often have deep backstories related to the history of the RPG world.
The protagonist sword is definitely one of the most interesting characters. It has a unique perspective as a reincarnated object. Fran, the girl who wields the sword, is also very interesting. Her relationship with the sword and her growth as a character are engaging.