MiniMax API v1 added support for character reference for the image endpoint POST images/create.
Example
CURL
curl --location 'https://api.useapi.net/v1-dev/minimax/images/create' \
--header 'Authorization: Bearer user:1234-abcdefghijklm' \
--form 'prompt="Freakish-looking clown wearing a red MAGA baseball cap and holding a large orange sparkling air balloon in his right hand. We see large graffiti behind him on the wall saying \"BEAUTIFooL TARIFFS\""' \
--form 'quantity="4"' \
--form 'aspectRatio="9:16"' \
--form 'characterFileId="user:1234-minimax:1234567890-file:1234567890"'
Result