Credits:

Author: Jockum Skoglund (hipshot)
The cloudy skybox
https://opengameart.org/content/stormy-days-skybox

Author: vladislavzh
The retro ocean skybox
https://opengameart.org/content/retro-skyboxes-pack

Author: Ulukai
Eclipse and Nebula skybox
https://opengameart.org/content/ulukais-space-skyboxes

Author: bean(alwayshasbean)
Maxwell the cat
https://sketchfab.com/3d-models/maxwell-the-cat-dingus-2ca7f3c1957847d6a145fc35de9046b0

Author: 雨宮レン
Hatsune Miku
https://sketchfab.com/3d-models/hatsune-miku-92448dece7d2479c8169bd5620057cf9