I understand little to nothing about the Stone Tentacle-Key, but from what I know about the Manager and his personal past, I want to narrow down our options for the Key’s placer. Major spoilers for Nemesis and Heart’s Desire ambitions, as well as general lore for the story and an all-around long winded ramble. TL;DR : My guess is the King of a Hundred Hearts.
[spoiler]When paying the Manager with the Key for advice on the Heart’s Desire ambition, he talks to it as though it were a lost lover, showing surprise at the smell of well water and mentioning how he must give them up once again, stating how he is not yet ready to bear that weight once more. Considering his past issues with love and the title of the outcome being "A hundred hands", I presume he’s talking to the key as though it were The King of a Hundred Hearts, his past lover whose life was bought with the First City. Though we’re short on information about the key and what little info we have feels disconnected, what I could find seems to indicate the Key as having value in matters of essence and dreams. When selling off the Key to Iron Republic devils for access to a room in the Nemesis ambition, the devil states that the price for entry varies from the proof of an aunt’s demise, two ounces minimum of the occupant’s liver, a soul of V.S.A.H. quality or better (presumably high?), or the Key itself. The majority of these items seem to hold some value of human ownership or part of a person’s self, especially the mention of a high quality soul, which the King’s might plausibly fall under. Having been gifted abominable immortality and shattered in heart and soul across his Clay Men creations, any significant piece of the King’s being would mean ownership to a fraction of his whole and potentially hold special interest to an infernal creature. The only other place in which I can find any lore of significance on the Key is when experiencing a honey dream, once again during the Nemesis ambition, where sentient roses crowd around a similarly shaped Key amidst a field of lion bones. Since the King is now more spirit or mind than physical body, and he is known for creating his Clay Men from his dreams and forming the Unfinished from his nightmares, the Key in the dream may some part of him within the dream world of Parabola.
EDIT: It just occurred to me that the Key could have a double meaning as the key to his heart and the key to his city. The heart part could be a nod to his namesake, which was fragmented along with his being into bits long ago. Since my interpretation of the King’s existence is that he lives dispersed among the remnants of his city in Polythreme and across all that he has given life to, like a spiritual force or a broken god, having a key to his city might quite literally mean having the key to himself. Hence, the Key being the key to his heart and his city, and in essence the King of a Hundred Hearts.
All of this is a large stretch on my part, but with no present alternatives, my best guess as to the Key’s placer would be the King of a Hundred Hearts himself. Considering the importance of Hunter’s Keep in Sunless Sea’s story involving the Tireless Mechanic (it is said that the Writhing River of Parabola flows "near" the Keep), there’s the possibility that the King could have placed the Key there on his journey out to zee or through the Writhing River’s side of the fence and into the real world. Whether this was by mistake or by intention, and for whatever reason this could be (do you think it could have to do with his incorporeal nature or the Clay Men’s relation to dreams?), he’s the only choice I can come up with at this time. It’s hardly solid proof, but there are enough "maybes" and "what-ifs" that I’m willing to pin him as my answer if only to have something written down. Unless the upcoming ending for the Season of Adorations or July’s ES provide any last minute clues, the King of a Hundred Hearts seems like the most reliable option.[/spoiler]
edited by Sir Joseph Marlen on 6/8/2018