One likely narrator could be one of Epsilon's closest comrades. For example, if it was someone like Church, who had a deep connection with Epsilon, they could be narrating their thoughts and feelings during and after his death. This would give an insider's perspective on the loss and the significance of Epsilon's role.
One common theme could be the exploration of loss and grief among the characters. Since Epsilon's death is a significant event, the fanfiction might focus on how the other characters in Red vs Blue deal with the emotional aftermath. They could be shown struggling to come to terms with his death, and there might be a sense of emptiness in the group dynamic.
One interesting plotline could be the characters from Red vs Blue having to adapt to the rules and scenarios of the Death Battle world. For example, they might struggle with the different power levels and fighting styles they encounter. Another could be a team - up between characters from both universes against a common, powerful enemy. It could also involve the Red vs Blue characters learning new combat techniques from watching the Death Battle fights.
Tucker is often a popular character. His unique sword and his somewhat cocky attitude make him stand out. Church is also quite popular. His sarcastic remarks and his mysterious backstory add to his appeal in these fanfictions. And then there's Caboose. His naive yet endearing nature can create some really interesting interactions, especially when paired with the more serious or battle - hardened characters from the Death Battle universe.
Batwoman is portrayed as gay in comics. Her sexuality is an integral part of her character and has been explored in various comic issues and storylines.