Thank you for clarifying.
Just to make sure I understand correctly:
The asset would be used as the playable character sprite during normal 2D action gameplay.
If the player is defeated, the game may show optional adult/R18 still illustrations of the same playable character, but those still images would be separately commissioned from another artist. They would not use, edit, trace, or adapt your pixel art.
Your pixel art itself would not be modified into adult content, would not appear in explicit scenes, and would not be used in adult promotional images.
Would this still be acceptable, or would you prefer that your asset not represent a character who appears in adult/R18 events at all?