One way could be through his diplomatic skills. Harry might be able to negotiate with the goblins in a very fair and respectful way. He could understand their concerns and offer solutions that benefit both parties. This would make the goblins see him as an intelligent and reliable person.
Since lemon fanfics are inappropriate, we should focus on their general characteristics from the official story. Asta is highly determined and energetic, always striving hard despite his lack of magic initially. Yuno, on the other hand, is more calm and has a natural talent for magic. They both have a strong bond as rivals and friends.
It could be about a boy with some extraordinary physical feature (big penis being a very odd and inappropriate way to describe in a normal context here) doing something amazing at the beach like rescuing a drowning person, which impresses everyone there.
Noelle could be a great addition. Her water magic is quite powerful and she has a complex relationship with both Asta and Yuno. She could be a source of both support and conflict in the fanfic. Another good character is Luck. His lightning magic and his rather unpredictable nature can add a lot of action and excitement to the story.
Asta would likely bring a new level of determination to the Crimson Lions. His never - give - up attitude could inspire the team members during tough battles.
Asta is still alive in the manga. The story keeps evolving with him at the center of the action. There have been many difficult situations, but he manages to overcome them without dying.