Well, without having read the 'anduin short story', it might cover various aspects. It could be a fantasy story where Anduin is on a quest to save his kingdom from an evil force. Maybe it details his growth as a person or his struggles against difficult odds.
One character that would be fascinating is Medivh. As a powerful mage with knowledge of time and magic, he could either be a helper or a hindrance to Anduin. He might know secrets about the time travel that Anduin is doing and use it to his own ends. Another interesting addition could be Illidan Stormrage. His complex relationship with power and his own past actions could make for some intense interactions with Anduin as he travels through time.
I'm not sure which one is the absolute best as it depends on personal taste. However, 'Anduin's Journey' is quite popular. It has a great plot that focuses on Anduin's adventures and his interactions with other characters. The slash aspect is subtly woven into the story, adding an interesting layer to his relationships.
Character development is a key element. For example, showing how Anduin grows as a leader through his interactions with Alexstrasza. Also, the relationship between them, whether it's friendship, mentorship, or a more complex bond.
The theme of light and hope is also prevalent. Both Anduin and Naru are associated with positive values, and their stories in the fanfic usually revolve around bringing hope to their people. It could be through fighting against dark forces or inspiring others to be better.
Well, he could become corrupted. Frostmourne has a history of corrupting those who wield it. Anduin, being a paladin, his struggle between the light and the dark could be a central theme. Maybe he starts to question his beliefs in the light.
One interesting Anduin Dark Side fanfiction could be about his fall from grace due to the influence of some dark magic or a corrupting force. It might show him making decisions that go against his usual benevolent nature, like allying with the wrong side in a war for power.
Power and responsibility is also a theme. Anduin, as a leader, has to make tough decisions, and the Jade Dragon often has great power. Their interactions in handling power and responsibility are explored. For example, in some stories, the Jade Dragon has to teach Anduin how to control a new power he has acquired. The stories usually show how they grow in terms of understanding their roles better through these experiences.
A plotline could involve the female Turren being in some sort of danger, and Anduin coming to her rescue. This could lead to a series of events where she then joins him on his quest to bring peace or justice to their realm. Or perhaps they start off as rivals, competing for a certain goal or position. But as they get to know each other better, they realize they have more in common than they thought and end up working together. Anduin could also be in a position of power and the female Turren could be an advisor of sorts, and their relationship could be a complex one of mutual respect and hidden feelings.