If you have issues with the engine, make sure you're using the latest available version. You can update the core package using Unity Asset Store interface:
Window -> Asset Store. In case you're using any of the engine extensions, download the latest packages using following links:
If updating didn't help, try to re-install the package by deleting
Naninovel folder from the project and re-importing it from the Asset Store. Be aware that by deleting the package folder you'll lose all the engine configuration data; you can keep the configuration by migrating
Naninovel/Resources/Naninovel/Configuration folder to the new package installation folder.
Always remember to backup your project (or use a VCS) before updating or deleting a package.
Haruhi God knows what could happen in the process.
In case the above steps didn't help to resolve the issue, check the issue tracker — chances are the problem is already being worked on. You can also create new issues there to ask a question or report a bug. When reporting a bug, please use bug template and fill in the required information.