And the hyperbole of being as fast as lightning is so synonymous with him they even named a whole video game after it:
Cars: Fast as Lightning
Yes, but that film is based on a race of cars, which in principle cannot go beyond a certain speed, so saying that a car is as fast as lightning is obviously a Hyperbole which only serves to emphasize the film etc, like when in advertisements they say: "the best product ever", that too is a Hyperbole made to emphasize the product, here too, it is a Hyperbole to emphasize the film, which is very different, because a Hyperbole does not contain contexts, and it explanations in most cases, it's just a ridiculous statement. An example in DS, Tengen stated to be the god of holidays, that is a Hyperbole made clear, also it is made by a character, this gives more consistency on the fact that it is a Hyperbole, and I repeat, a Hyperbole is made clear to be precisely a Hyperbole, a comic and humorous context, in fact Hyperbole by definition, and how to use it in writing, the author must make it clear that he is intending it in a Hyperbolic way.
Let's take the last example, you look out the window and see a bicycle race, you see someone going very fast, and you exclaim that he was going as fast as the wind, that is clearly a Hyperbole, for two reasons.
1. You are objectively emphasizing the speed of that bike rider, because you saw him going fast from your perspective
2. A bike cannot objectively go as fast as the wind
- Zenitsu's statement is very different, first of all it is not a character who comments on Zenitsu's speed, but it is directly a narrative statement, and if someone says "But the author is a person like us", obviously yes he is, but he is not commenting, he is explaining, the movement of Zenitsu, which is different, and also a narrative statement in general, obviously it can make rhetorical figures, but it is already less probable from my point of view, because the narrative tends to explain in many cases. And for example in a Databook, where the objective is to explain concepts of the verse etc it is unlikely to be a Hyperbole
- It is not impossible for Zenitsu to go to MSH+. The DS characters have the feat of the fact that they can already go faster than sound, but in general reach absurd speeds, so already the physics is contradicted and reduces the possibility of the fact that it is a Hyperbole, since the LS Hyperbolas are based on the fact that they cannot go at that speed on a physical level, and since we cannot know the author's intentions for me we can take the slightly more probable choice, which is that it is not a Hyperbole.
If we want to add more consistency it is the fact that Zenitsu, in a very narrative way, is represented just as fast as lightning, and furthermore, following the amp that gives the mark which is
apparently 10x, would take Tanjiro from MSH to MSH+ and all the verse. So i think the statements are pretty consistents.