Another possible storyline is Gilgamesh having a conflict with an ancient evil that has resurfaced in the Marvel universe. Maybe an old enemy from his own time that has found a way to return. He would then have to use his powers, which could be enhanced versions of his historical feats in the Epic of Gilgamesh, to defeat this enemy and protect the modern world from destruction.
In Marvel fanfiction, Gilgamesh is often more of a superhero - like figure compared to his original mythological self. He may have enhanced physical abilities and be more directly involved in modern - day battles. For example, his strength might be on par with the Hulk in some stories.
Gilgamesh can be portrayed as a powerful and haughty figure. He could walk around the world of Danmachi with an air of superiority, looking down on the 'lesser' adventurers. His flamboyant style and his love for grandeur can be emphasized, like always wearing the most elaborate and expensive armor.
The Epic of Gilgamesh was one of the famous works of ancient Chinese literature and an important chapter in the history of world literature. The following is the translation of the full text:
The Epic of Gilgamesh was a work of ancient Chinese literature. It was a biography of Khan Gheng Khan in ancient China. The epic was written in the 10th century B.C. and recounts the heroic deeds of Khan Gheng Khan in conquering Central Asia and South Asia. The epic had an important position in Chinese culture and was regarded as one of the representative works of ancient Chinese literature.
In the story, they start as sort of rivals. Gilgamesh is a powerful king who is a bit wild, and when Enkidu is created, he challenges Gilgamesh. But then they become friends. They share a deep bond that is tested through various trials. For example, when they face Humbaba, the demon of the cedar forest. Their relationship is complex and full of mutual respect in the end, and Enkidu's death deeply affects Gilgamesh.
The graphic novel presents Gilgamesh as a complex character. He is initially a powerful but somewhat tyrannical king. Then, through his friendship with Enkidu, he begins to change and shows more empathy.
He would likely be portrayed as arrogant. Given his status as a powerful and ancient figure in his original lore, in DxD fanfiction he would probably look down on most of the characters. He would act as if he is above the petty squabbles of the DxD world.
He could be integrated as a powerful enemy at first. He might target the academies because he sees them as places that are trying to control and limit power, which goes against his own philosophy. However, as the story progresses, he could have a change of heart after seeing the selfless acts of the RWBY characters. He could then use his powers to help them against a common enemy like Salem.