This is the most underrated manga I've seen on mangadex. It has plot, realistic characters, artwork could be more detailed but is ok, very atmospheric. Reminds me of Tropical Citron.
To me it is apparent that Sakuya was a cat. What @Yunefia summed up proves this enough I believe. Besides this is not kind of gloomy manga where real children (with hair longer than themselves) appear lying on the bare ground under the house naked.
This picture from chapter 17 is also probably...