A known bug that was reported to me from somewhere else:
A Ren'Py error may occur during an event on the first day of Act 3, should the player choose to partner with Kagami. You can ignore this error without having any lasting effects. (It happens because of a bad ATL transition call, so you may not even see it if you are skipping text.) This bug should now be fixed in the development build, and the fix should eventually be rolled out in a patch. (Timeframe to be determined by any further bug reports.)