Yes, it's from Indo-Pacific since I live in the Philippines.
The specimen is almost exactly the same when it's still living (same color, shape, but with deformed organs on the lower body). I'm already guessing that it could be a sea cucumber but I just can't compare it to all the sea cucumbers that I've found. It doesn't behave like one although many sea cucumbers have different features. I've been searching for the exact species for years but unsuccessful.
Thanks for the reply!
Hopefully, someone can identify the chiton...
I found out that the chiton is Stenoplax alata based on Poppe-Images: