I'm not sure which specific novel 'Luna Ares' is from. It could be a character created by an indie author or from a relatively niche piece of literature. Without more context, it's hard to say exactly who this Luna Ares is in the novel.
Well, characters like Thor, with his godly powers and Mjolnir, or Thanos with his immense strength and intelligence, might have a chance against Wanda in the comics. It often depends on the specific circumstances and plotlines.
Ares himself is a main character. And Aphrodite often features as she had a relationship with him. Also, other gods like Zeus, his father, and Athena, who was also associated with war in a different way, could be important characters in ares stories.
Sadly, I have no information regarding the author of 'ares cries fanfic'. It could be an amateur writer who just wanted to explore the character of Ares in this way and shared it in a fanfic community. Or it could be someone with more experience in writing fanfiction, but without further details, we can't tell.
There could be Clarisse. Since she is Ares' daughter in the original Percy Jackson series, she might play an important role. She could be either jealous of Percy getting her father's attention or become a sort of mentor - like figure to him. Another character could be Annabeth. She might be worried about Percy being adopted by Ares and try to rescue him or at least check on him regularly.
In the light novel, there are a few powerful characters who might have a chance to defeat Rimuru, but it depends on various factors like the circumstances and their own powers.
To develop Ares, show his internal conflict. He's the god of war, but he could have moments of doubt about the destruction he causes. For example, after a particularly bloody battle, he might question if war is always the answer.
As I don't know the exact 'ares graphic novel', but likely Ares himself would be a main character. There might also be other gods like Zeus or Athena if the story involves the Greek pantheon's politics or conflicts.
In the 'ares original story', Ares is of course the central figure. Then there are his divine counterparts. Aphrodite was his lover in some stories, and their relationship added a different dimension to his character. Hermes also had some dealings with Ares. Among mortals, there were those like Achilles. Ares' influence on Achilles' life and actions in war was significant, making Achilles an important character in relation to Ares' story.