The Forest of Einnashe (腑海林アインナッシュ, Fukairin Ainnasshu?, lit. "Disembowling Sea of Trees Einnashe"), also known as Demon of the Schwartzwald (シュバルツバルトの魔物, Shubarutsubaruto no Mamono?), the Thinking Forest (思考林, Shikō-rin?), and Predator Forest (動き襲い捕食する森, Ugoki Osoi Hoshoku suru Mori?), is an 800-year-old sentient forest that ranks seventh out of The Twenty-seven Dead Apostle Ancestors. It is the main focus of the story, Talk.
The previous seventh ranked Ancestor, Einnashe, was a magus who transformed himself into a Dead Apostle. He was a specialist in hypnotism able to use his Reality Marble, which allowed for "memory remodeling", to manipulate the memories of everyone he encountered, including Arcueid Brunestud, with such precision to make them entirely forget his existence. The suggestions worked on the basis of "understanding", having told her "There is no Dead Apostle Einnashe", so Len's master was able to dive into Arcueid's subconscious to make the order impossible to recall, allowing the information on Einnashe to resurface. Arcueid killed Einnashe and his entire clan, and she carelessly left his body under a bloodsucking tree, which accidentally sucked the Dead Apostle's blood over time and transformed the entire forest into a Phantasmal Species, the second generation of the vampire Einnashe.
The Forest of Einnashe began to manifest itself every fifty years since that time, taking blood with even the Church being unable to stop it. There were many organizations seeking to use it or destroy it, and not a single person was confirmed to leave alive. It was one such Dead Apostle that ignored balancing the need for blood and sustainability of the society from which it fed due to its nature, having sucked blood with reckless abundance since the Middle Ages. Though it sucked blood with abandon, its unique nature that made it hard to kill and their many unsuccessful attempts led to the Church deciding to begin sending people to slay it when it manifested only as a formality. They did not know about Einnashe's death, so it was thought that he had simply changed dramatically. They believed that it was a product of his Reality Marble, lasting an unnaturally long time until he was satiated.
Though it has a mind and will, it does not appear to display sentience, and it only attacks and reacts based upon instinct. Though there have been those trying to negotiate with it or capture it, is not able to distinguish between friend or foe, marking everything that sets foot within it as mere food. It is able to sense that something capable of killing it approaches, causing it to fly into a frenzy and attempt to kill those within.
Einnashe becomes active sometime after the events of Tsukihime, quickly completely draining two towns. Over one hundred people seeking its fruit enter within a period of four days, with none returning. Ciel is sent to slay Einnashe under orders from Narbareck, and she finds the bodies of the members of the Church sent to eliminate it. Though they had numbered forty people, not one was able to survive a single night, and the final stand of ten men, all first-class fighting monks, could only destroy a small section of the forest. Merem Solomon also arrives, watching Ciel, and they tenuously proceed into the forest.
Shiki Tohno also arrives separately, searching for the fruit for Arcueid Brunestud, and encounters Forte, a magus from the Mage's Association. After Shiki dispatches her, Merem Solomon appears before him as a disembodied voice, telling Shiki that he will guide him to Einnashe's core in exchange for learning the truth behind the forest because he knows of Einnashe's death. Shiki tells him of Arcueid's blunder, and he makes his way to the core. The forest begins to rampage upon Shiki's approach, easily killing Merem's daemon and attacking Ciel, but fails to save itself as Shiki ends its life. The forest itself is still left intact after its death, as those remaining alive leave it.
Einnashe has the form of a black forest, best described as an alien world shrouded by darkness even in daylight, fifty kilometers in diameter. It has transformed into a massive predatory being with a mind and will, causing it to "move" over entire areas and towns, and absorb all the blood from the creatures and people within the area. It hibernates for decades, generally manifesting once every fifty years to absorb hundreds of victims, and it is constantly sprouting entirely new areas of forest. It does not simply prey on humans, but entire villages and animals as well.
While it is inactive, the tree branches are sufficient to wound creatures even while still, and they are able to assault prey with the intent to kill once it becomes active. Anything unfortunate enough to find itself inside within the forest of instruments of death is collectively attacked by the trees and plants, acting like free-form weapons, from all angles, and even something as large as Merem Solomon's two hundred meter Daemon of the Right Leg is completely swarmed and covered within a minute. The only way to remain safe is to destroy the trees down to their roots to keep it from moving in a particular area. The air can also become poisonous to cut off all escape those who enter, so all who have been caught have never survived. Merem comments that the soil of the forest works well as food for his daemons.
Once it becomes active, blood from its victims flows through the forest, causing its entirety to flash with a dark-red coloration resembling an animal's innards. It is not produced inside the forest, but taken from the victims entering from outside. Blood purfuses all the branches and roots, making the scenery resemble Hell itself. The roots and trees secrete blood as if it were sap, and the forest constantly growls like a bloodthirsty beast. There is a single red fruit, the Fruit of Einnashe, growing on a giant tree, the throne of Einnashe, within the forest's center which can grant a person temporary immortality, having become the essence of the harvested blood of its victims and the thousands of animals that once inhabited the forest. Merem believes that a vampire could restrain their bloodlust by eating it. This acts as a light trap that has drawn a countless number of people into the forest to never return. Once the fruit is ripe, it begins dripping blood. Within the droplets are seeds that germinate in the earth before sprouting into smaller vampiric forests that are called Children of Einnashe. Unlike the Forest of Einnashe which appears every fifty years, a Child of Einnashe appears only once.
Being classified in the top ten ranks of the Ancestors and one of the most powerful, the entire forest is a living being unable to be killed by normal concepts, and its core is impossible to find due to the constant movement of the forest. Its size is not incredibly large, but it is not possible to locate something that does not stay in place within the time it stays manifested. The forest, as a phantasmal species, feeds off the natural environmental magical energy, making it nearly impossible for magecraft and similar abilities to be used within its confines. Even if people possess Magic Circuits, they will not function due to energy being dominated by Einnashe. Only personal abilities can be used, while supernatural powers that rely on exterior energy are sealed. The Church's Executors, even those specializing in close combat, have no ability to stand against it, and magi would have similar trouble.
Kagetsu Tohya - 27 Dead Apostle Ancestors Series, ７／Einnashe
Used to be a normal Dead Apostle. The current Einnnashe is of the second generation.
 Tsukihime Dokuhon PlusPeriod - talk. Glossary: Einnashe [Person's name], p.195
Einnashe [Person's name]
A member of the Twenty-Seven Dead Apostle Ancestors. Number Seven.
Most Dead Apostles were concerned about balancing their needs for blood and the sustainability of the society, but there were also Dead Apostles with values unchanged since the Middle Ages and sucked blood with reckless abundance.
Einnashe was such a Dead Apostle.
However, due to its peculiar nature, it was difficult to eliminate it. As a result, it was currently siphoning blood without control.
It was thought to be a Reality Marble.
 Tsukihime Dokuhon PlusPeriod - talk. Glossary: The Engulfing Forest [Colloquial Term • Title]
The Engulfing Forest [Colloquial Term • Title]
The common name of Einnashe. It was also called the Sentient Forest.
A magical creature that was active every fifty years. It was a blood-sucking demonic forest that not only targets humans, but also other creatures that dared to tread into it.
The forest was filled with instruments of death. The tree branches were sufficient to wound creatures even when still, but while Ennashe was active, they all assaulted with the intent to kill. One can only imagine the view of such an alien realm.
During periods of activity, blood began to perfuse all the branches and roots. They entire forest flashed dark red. The scenery could be said to be Hell itself.
It was thought to be a Reality Marble.