Filou and Tigris play much less if I compare it to their kittenhood. And sometimes they are blocking each other: e.g. Filou comes in my room and asks me to play with him. I start throwing mousies, Filou runs like crazy, then Tigris shows up. Just sitting in the door, watching.

And Filou stops and walks under the chair. Watching too

This can work the other way round as well.

One thing is: they have moments during the day for everything: time for napping, time for cuddling and a time for playing. If it's the right moment, then it can be either a short play or a longer or more energetic play. But if it's not the right moment, then nothing will interest them.

And if you are not available to play with them in the right moment, then it happens that Filou plays by himself. Or they start a wrestling match.

They like new ideas. I got a gift these days and there were small branches knotted in the bow. Filou loved knacking these branches I always marinate a mousie in the catnip box: very interesting. A new box etc.

Filou in general is more playful than Tigris. Tigris is much lazier.

So I think on one hand Luna is a lazy girl, on the other hand maybe you don't know when she's in a playing mood. I don't think it is some depression. Not as long as she is cuddling and wrestling with her funny little sis