If you are referring to the shadow on their face from their hair, it is likely that they could be using the "Fake Shadow" feature that exists within liltoon.
https://x.com/elusyia/status/1780752783303491932
Here is an informative post explaining the feature and how to potentially add it to your model, though when trying to follow it I had some issues with my own model, hopefully you may have better luck.
OR
They may simply be using NGSS + PCS as most people on Twitter (X) use for photoshoots which can be found here:
https://booth.pm/en/items/4493526
