As can probably be seen by the response, the way the question is made can lead to misleading answers.
Akira was filmed completely using 24 distinct images per second to achieve 24 frames per second. This is normally called "shooting on ones", where no frames are repeated consecutively.
Most animation is done "on twos", which mean 12 distinct images per second are used to achieve 24 frames per second, by repeating as necessary.
Most Anime is done from 2 to 12 distinct images per second to achieve 24 frames per second, by repeating as necessary.
High-Quality studios usually use a mix, having some animation running on ones but the majority of the feature running on twos (Ghibly, for example, does this a lot, usually it's very obvious in the smoothness of the animation).
Akira is the most famous animated full feature done in "true" 24fps for the whole length of the movie. I'd argue the other most famous one is the unreleased "The Thief and the Cobbler", partly due to its bizarre history and partly because when talking about the fact that it's done "on ones" is always mentioned.
So the answer to your question is, if taken literally, that no, it's not the only one "filmed" at 24fps (most, if not all, are).
The answer to your actual question is "yes", as it's the only full-length anime production animated on ones, at the full 24fps.
Depending on whether you want to consider "The Thief and the Cobbler" (being as it is unreleased), it is the only "modern" (post-1950) full-length animated feature animated on ones.
I would've given the willfully obtuse answer to your literal question instead of your intended question, but I see that's been done already :)