He could become interested in the characters from Death Battle that he hadn't known much about before. The fanfiction might introduce him to new storylines and relationships within the Death Battle universe. This could potentially influence his view of the overall concept of Death Battle, perhaps making him more or less interested in it depending on the quality and nature of the fanfiction he reads.
I'm not sure specifically as there could be many novels with such a title. Generally, it might involve a death knight who has some sort of lordship or power. Maybe it's about his battles, his rise to power, or his conflicts with other forces in a fantasy world.
The Death Knights in the Overlord novel are powerful undead warriors. They are often depicted as having great physical strength and being highly resistant to damage. They are loyal servants of the overlord and play important roles in battles and the overall power structure within the story.
Since I haven't read it, I can't say for sure. But it might have the death knight himself as a main character, of course. There could also be characters like his loyal servants, perhaps other powerful dark mages or warriors who serve him or oppose him.
Sebas Tian is also a notable character. He is a butler - like figure with great strength and a sense of honor. He is involved in various missions and interactions, and his relationship with other characters, especially his loyalty to Ainz, is an important aspect of the story.