One great ikaris fanfic could be about his adventures in a different realm. It might explore his relationships with other characters in new settings, like how he teams up with a mysterious ally to fight an unknown evil.
Well, it's not that straightforward. Ikaris' character is morally ambiguous in the comics. His motives and actions can be interpreted differently by different readers.
To start an ikaris fanfic, think about the setting. You could place him in a modern - day city or a post - apocalyptic world. Then, create a plot that challenges him. For example, he has to protect a group of innocent people from a new threat while adjusting to the new environment.