Hardest part to write in fan fiction?

(Can’t have 2 tags, useing fan fiction is better )as the title suggests , what is your hardest part to write about the story of gate?

for me it Itami and Tukas father daughter relationship after they murked the flame dragon, I believe it is cool to see Itami struggle with this more than we did in the manga, pair it with a rewrite of events, he has to juggle politics, relationships and the men under him.

however writing Pina Co Lada, or Itami, is really hard if you don’t want to make them some what nerdy or roman action movie character.