What is the Endosomatic heart and how do I get it? I've played through a couple times and haven't found it, and would really like to unlock the 'play' button in the ghostiary.
As stated in my guide, the endosomatic heart is a bleeding heart that can be purchased at the shop, which allows Japes to "feed" his health to ghosts by not struggling, indicated by the pink heart that shows up in place of the struggle icon near your health bar when you let the digestion play out. Once this happens, you will no longer lose health, and once you struggle free, you will usually get some new dialogue, items, and a fed entry. To feed Zahara safely, change her Json to this:
"love_value": 100,
"love_value_until_defeat": 1000,
Otherwise, she will cause an instant K.O. Don't do it to Waboomi, Mitsuro, Honeygast, and especially not the Evil "Ghost" with a different health bar, because they will just kill you.