I haven't watched Fate/Zero so I can't comment on the story, but here are my thoughts on the prose from a quick glance at it. I'm still pretty new at writing myself so take it with a grain of salt. You identify characters by descriptions such as when you refer to Alexander as "the red-haired man", which is annoying to read. Stick to the character's name or pronouns such as "he" or "she". In Lina's section you use her name too often even when it's not necessary. When it's already clear from the previous sentences that you're referring to Lina, then use "she". Use names when it could be confusing who you're referring to. You use numbers sometimes, and maybe it's just personal preference but I think that unless the number is large it's better to write the name of the number, so "seven" instead of 7. Also, it's grammatically incorrect to start a sentence with a number.

The line "gasped with revelation" should probably be "gasped at the revelation." The line "Thank you, Emiya Kiritsugu..." is missing a quotation mark. Also, in my opinion a character shouldn't address someone else by their full name unless they're either mocking them, being playful, or specifically pointing out that they know their name. This case seems to be the latter, but I'm just mentioning this to keep in mind in the future because a lot of stories overuse this and personally I find it annoying and immersion breaking since no one does this in real life. The other main thing is that while you do a good amount of showing, you also do some telling. For example, in the line 'Emiya's smile was sad, and didn't reach his eyes' we can infer that the smile was sad since it didn't reach his eyes, so you don't need to tell us he was sad. Also, in the line "they were doomed. cursed" you need to capitalize "cursed". Other than that, the prose seems pretty good so far. For the first thing you've written, it's very good.