How to restore the blurred out curvy outlining

[themon-master]

I'm trying to restore this episode from an anime series,
and the only thing I have problems is restoring is this weird blurry outlining which only appears on the curvy areas (Look on the highlighted areas).

[Attachment 92902 - Click to enlarge]
I can't find a script that restores the problem without causing any over-filtering artifacts on the other areas.
Can anyone help me out here?
Thank you!
https://drive.google.com/file/d/1VlHWFbefeiY4TnEy2XJzG9SxWn8sBAf-/view?usp=drive_link

[Selur]

One could probably:
1. downscale
2. upscale with a better resizer
3. use an edgemask and replace the edges of the source with the upscaled one
or first blur and then darken and sharpen the lines.
or sharpen and darken,..
just Sharpening and Darkening
script: https://pastebin.com/6sVcmN8b
image: https://imgi.co/c/qAPc6WN


Depending on what counts as ' over-filtering artifacts' you will to either write some clever custom Vapoursynth or Avisynth code or use some machine learning model (https://openmodeldb.info/) or similar,...

using DPIR Denoise (a machine learning filter) on the edges, then applying darkening and sharpening
script: https://pastebin.com/2Js7c1Cc
image: https://imgi.co/c/5fPYrlZ



Cu Selur

[jagabo]

Use mt_edge() and a custom matrix to build a mask of diagonal edges. Then use that mask with Overlay() to apply a sharpened image only to those areas.