Wow, the author of this fanfiction fully does not realize how fountain pens work at all. Which is fine: all you had to do was not touch on how the pen worked and nobody would have noticed! Or you could've looked it up.

Or anything other than describing red ink writing that was done with a fountain pen as "a red fountain pen".

Bonus info: fountain pen ink dries up in the pen, which can ruin it if you're not lucky, if it lies unused for long enough (how long to dry up depends on the pen, and it's longer if stored point-down, but it can be as little as less than a week; it takes longer than that to ruin a pen, though). Fountain pen ink in the bottle also degrades over time. It can spoil or grow micro organisms and also can break down chemically, but evaporation is perhaps the biggest risk. The hobbyist sphere seems to agree that typical shelf life is "ten to sixty years" (optimally: in glass, sealed as airtight as possible, protected from heat and light and no contaminants introduced), so it's not impossible you could still use ink from a bottle from the 1940s, but it's highly unlikely.