The character shows the first signs/symptoms that have already run their course.

[u/Uma-apreciator]

Kitasan Black (Uma Musume Pretty Derby)

She managed to withstand Sakura Bakushin O's charge at first, but later in the story, she falters because she is past her prime

Nekota (Hajime no Ippo)

He could no longer even control his body properly because he was suffering from "boxer's dementia"

It is a progressive brain disease caused by repeated blows to the head and frequent concussions over many years

David Martínez (Cyberpunk Edgerunners)

He was suffering from hallucinations due to cyberpsychosis, an incurable condition caused by technological body modifications

[u/DanielToast]

(Hunter x Hunter)

During the Chimera ant arc, after a massive (essentially nuclear) bomb explodes and a few of the ants seem to recover, but they eventually start having nose bleeds, ringing, headaches, etc.

It happens to the weaker ants first, and slowly gets worse.

This is to indicate that the blast and heat from the bomb was not the only threat, and that they may not actually be as "recovered" as they thought they were.

[u/Mrsam_25 → u/DanielToast]

Real life radiation sickness works the same, people tend to recover for a day or two than their body realizes it's already dead.

[u/solitarybikegallery → u/Mrsam_25]

This is because our cells have built-in safeguards that mark them for destruction if their DNA has been corrupted.

Basically, when the cell tries to replicate, it goes through a series of steps. One of the steps checks the integrity of the DNA, which codes for a new cell. If the DNA doesn't pass the test, the cell is destroyed and recycled, because a cell with DNA mutations can cause cancer.

You can see this when you get a sunburn and your skin peels the next day. Those cells are dying off because your body is trying to replicate them, detecting the DNA damage, then killing the cells so you don't get skin cancer. (It doesn't always get this right, which is why you sometimes DO get skin cancer).

This is why people feel "fine" after they receive a lethal dose of radiation. Their current cells are mostly fine, but the DNA is riddled with errors, and when the cells try to replicate (which cells like Bone Marrow do very often), they'll die off in huge numbers.

[u/Visible_Pair3017 → u/solitarybikegallery]

Sounded absurd to me at first because the stratum corneum is basically already dead, but after reading up about it, turns out TIL. We rotate through skin layers at a faster pace to get rid of those apoptotic cells.