I'm using 3D models in my project and a custom UI camera. In the game the player interacts with this objects and, if it clicks on one of them, the dialogue UI will show up. There are three cameras: a main perspective camera, which can be rotated by the player, and the camera manager and custom UI cameras, which are ortographic

When backgrounds or characters are spawned, they overlap with the 3D models. I suspects this happens because they're instantiated outside of the canvas (content object of custom UI). Is there a way to tell Unity/Naninovel that sprites are part of the canvas? I can't reposition the models because of lighting issues, which I have no control of because the models were given to me.

If you want an actor to become part of the canvas, there's Render to Texture which will render a non-generic character onto a texture which can be used in many ways, including custom UI. Be aware though that there are some limitations such as no transform controls but that can be easily fixed with a custom command. More information can be found here: https://naninovel.com/guide/characters. ... to-texture