Firstly, I think you're brimming with great ideas. Secondly, I'd like to add on.
- The boss introduction can be all of the "destroy the heart" texts compiled into one big text that gets clawed and disintegrates into the cat
- I like the suggestion of the mockery for absolving monsters, and I think that having something similar for executing would be good. Maybe if you execute a lot the text would start questioning if the player is "preparing for something". Or, after a lot of executing, the game text stops appearing altogether and only shows up here and there to urge the player onwards.
- Since some players might be inclined to only absolve the first time through, the game should force the player to fully absolve more than once and only after playing the other endings (only execution and some-some) to add more engagement. Sounds Undertale-like, yeah, but it succeeded for a reason.
- The first only absolve would say that the player has not suffered for their own citizens enough.
- The second only absolve would tell the player that they are closer to "it" (the cat) and would tell the player to seek other methods before trying to only absolve again (it repeats this message if the other endings are not reached)
- The third only absolve would initiate a special sequence (dev can decide on this)
- As for the story I think it makes sense like you said that we were put in the forest since we were bad.
- We get more and more information about our past self for each different ending we achieve and after each only absolve the UI gets a little lighter in the beginning.