Well, in my opinion, Star Wars has the edge in fanfiction for this 'Warhammer 40k vs Star Wars' comparison. The concept of the Force is just so fascinating and offers a lot of room for creative exploration in fan stories. Also, the iconic characters like Luke Skywalker and Darth Vader are well - known and loved, which makes it easier for fans to write engaging stories. Whereas Warhammer 40k can be a bit more complex and intimidating for new writers in the fanfiction world.
Toge Inumaki is important too. His special cursed speech ability makes him stand out. Also, the principal of the school, Masamichi Yaga, is likely to be important as he is in a position of authority and has an influence on Gojo and the other students. There could be other characters like the members of different clans that also play roles in the complex web of the story.
It's really hard to say. In Warhammer 40k, there are extremely powerful Space Marines with advanced technology and psychic powers. However, in Star Wars, the Force gives Jedi and Sith incredible abilities. If it's a large - scale battle, the Imperium of Man in Warhammer 40k has a huge number of troops. But the Star Wars galaxy has the Death Star which can destroy planets. So it depends on the specific scenario written in the fanfic.
In Warhammer 40k, the Emperor is an extremely powerful character. His psychic powers are off the charts and he has a huge influence over the entire Imperium. In a face - off against Star Trek characters in fanfiction, he would be a formidable force. In Star Trek, Q is a very powerful being. He can manipulate reality at will. If Q were to engage with the Emperor, it would be a battle of two extremely powerful entities with different natures. Q's mischievous and almost omnipotent nature against the Emperor's more serious and controlling power would be quite a showdown.