zeidhan29
KK Master
Those are SD (Scene Data), they most likely came with zipmods that bring the assets without texture; The game (charastudio) does not really recognize them as maps but it is a very practical way to create or import scenarios from other games without wasting so much time in Unity.
Normally to make maps for koikatsu, you have to use the correct script and add the available zones for the H-Scenes; It is a more complex process.