Well, the demon lord himself is likely to be very interesting. He probably has a complex backstory that led him to become the demon lord. His motives might not be as straightforward as just being 'evil'.
The hero is also a key character. They often have to overcome great challenges and grow throughout the story. Their journey from an ordinary person to a hero is always fascinating to follow.
The titular greatest demon lord is definitely one of the most interesting. His journey from being a powerful and feared figure to being reborn and having to adapt is captivating.
The protagonist who is on a mission to defeat the demon lord for their daughter is surely one of the most interesting. Their determination and love for their daughter would make them stand out. Also, the demon lord itself could be very interesting. Its motives, powers, and backstory would add depth to the story.
Perhaps the people who interact with the reborn demon lord are interesting too. They might be ordinary folks who are unaware of his past. Their reactions to him and how they influence his new life could be very engaging. For example, a kind - hearted neighbor who befriends him without knowing his true origin.
Zenitsu is quite interesting. His cowardly nature at first, which is in contrast to his amazing lightning - based fighting skills when he's unconscious, creates a lot of comical and engaging moments in the light novel. Inosuke is also fascinating with his wild and boar - headed appearance and his brute - force fighting style.
Obviously, the demon lord is one of the main characters. They are likely to be at the center of the story, driving the plot forward with their actions and decisions.
Obviously, the demon lord is one of the main characters. There might also be his closest minions or advisors who play important roles.
Another theme might be friendship or the potential for it. Despite their opposing roles, there could be moments where the demon lord and the hero understand each other on a deeper level, blurring the lines between their two worlds.
I think Filo is an interesting character. She has a unique personality, being part human and part bird. Her naivete and her strong power make her stand out. Another interesting one is the Spear Hero. His initial rivalry and later complex relationship with the Shield Hero create a lot of interesting plot points.
The protagonist is usually quite interesting. They often have unique abilities or personalities that set them apart. Maybe a character who has a special power that no one else has. Another could be the mentor figure, if there is one, who has a lot of wisdom and a mysterious past.
The main character is the demon lord himself. He is a powerful and complex figure. There are also other characters like the various races' leaders who interact with him, such as the elven queen who has her own motives and agendas when dealing with the demon lord.