Agree, the gameplay is cool (I love the platformer, hide and seek + puzzle style), but the plot and ending are disappointing.
The two endings are: you can't save the sister, you flee the mansion, but a succubus (Emi) catches you and rape until you die. (normal ending)
You can't save the sister, you flee the mansion and return to your village , and an old lady tells you succubus army killed and raped everyone. (secret ending)
I think the dev really missed something with the cat girl; she becomes your friend and randomly gets kidnapped by the imp (blue-skinned girl) for no other reason than "I'm mad because you escaped from my trap so I drug your new friend with aphrodisiac." and
The gameplay is cool, it's funny to play with challenge, but I definitely don't play for the lore.