I really enjoyed The Undying Beast, well done Kira!
SPOILERS AHEAD!
My thoughts from this would be that I myself am the beast, I find myself at the end there and that whatever I do to others, those actions of mine only harm me in the end. Since there were dead animals with wounds, I'd assume they were killed, not just dead from natural causes, then I'd think that the game might imply that humanity is the undying beast. I'm not sure if the game shows any evidence to support whether this is about one person or just humans in general, I still like that it is left for interpretation or more playthroughs to uncover the story here.
I played 3 times, I saw a lot of new things on my 2nd play and even more on the 3rd, and I managed to get the 2nd ending on the third go and it makes me wonder what that means, since the grave is open but the flower is already growing there, maybe that's the ending where I actually don't "accept death" like it said in the menu. Or someone dug me out.
I might be completely wrong about any of this but I wanted to share my thoughts since games from Kira always have something hidden deeper in them.