Sprites:
https://ifthenelse-interactive.itch.io/
https://itch.io/c/2006928/my-free-visual-novel-characters-for-your-use
https://itch.io/c/1115123/new-style-free-to-use-assets
https://banya.itch.io/free-sprites-vn
https://itch.io/c/698965/yume-series-free-to-use-assets
https://cucurbitapepo.itch.io/girl-sprites-for-visual-novel
http://tokudaya.net/index.html
https://itch.io/c/2006931/fairytale-and-fantasy-character-packs
Backgrounds:
https://itch.io/c/4211158/background-and-item-asset-packs
https://katy133.itch.io/vn-asset-pack
https://tidalblossoms.itch.io/free-outdoor-visual-novel-backgrounds
https://noranekogames.itch.io/yumebackground
https://chibi785.itch.io/cafe-background
https://vision-renders.itch.io/
https://lemmasoft.renai.us/forums/viewtopic.php?f=52&t=17302
https://www7b.biglobe.ne.jp/~osumashi/free_bg.html
Other images:
GUI:
https://thaumaturge-art.itch.io/assets-fantasy-ui
https://tofurocks.itch.io/renpy-gui-template
https://loudeyes.itch.io/dating-sim-ui-pack
https://lunalucid.itch.io/free-character-creation-template-for-renpy