Memory Delving

Memory delving is an innate ability and practice of demons in the Seraph of the End series. Such beings can look into another individual's mind to essentially access any amount of information.

Background
A magical based capability, users can view memories as if in a virtual reality like environment. Where past events can be recollected differently, with parts not remembered at all by whose explicit memories they are, this capability is more equivalent to viewing a specific time period with previously unregistered details able to be looked at first-hand. The individual's memory is seen to be intact, where the only tampering comes from the demon themselves.

As part of their goal to possess their human host, demons often corrupt unsettling memories in an attempt to break down a human's mind and so make them susceptible to having their body taken over. A demon requires energy from the human they have a contract with in order to access memories. The further back memories are the more calories are required to view them. Other barriers include memories that have been removed which are not able to be seen by a demon.

Process
Physical constructs act as gateways within a memory, these can be circular spell-like circles, to literal large doors. An eye within Yu's memories was touched by Mika in order to access the perspective it had. Other memories, such as those from a similar time period can essentially be flicked from one to another. Mika can view a memory within Sanguinem and instantaneously bring one from outside within view without having to physically travel between each point. Energy is required to navigate a memory, Mika's tail would disappear when he and Yu were running low on it.

Story
The idea to resurrect everyone is part of the motivation for Yu and Mika planning to look into memories. Where Yu felt he had memories from before he was born, his memories were to be the ones accessed by Mika who had undergone the transformation from a vampire to a demon. Having secured a food supply needed for memory delving, Yu and Mika established themselves within the Sea of Trees around Mt. Fuji. It is here where Mika places his hand on Yu's chest for them both to enter memories from ancient Greece. This is done by Mika disappearing from the physical world, and then Yu too after closing his eyes to join him.

They appear as children in the memory which Mika feels is so less energy is used. While they cannot be seen or heard, Yu and Mika find they can still be affected by physical objects including the people there. This memory accessing brings up a scenario of Sika Madu with his disciples, including Krul and Asuramaru from the present times which is speculated to be because this is a mixed memory from Yu and Mika. In this memory environment, Mika can feel that the First is really far, and weak, so there is little chance of that demon being able to join them in the memory.

Able to walk around in the visualization of ancient Greece, both Yu and Mika can move themselves to the First's mansion and view the corpse of Mikaela kept there. By generating a spell circle like creation, and by consuming Yu's desires, Mika intends to force themselves to deeper past memories. Energy is required from Yu and when he returns to the memory having eaten, Mika has formed many floating circles which leaves him appearing weary.

A towering dark colored door forms the passage to even earlier memories. Having been able to glimpse them, Mika awaits for Yu to open the door. A verbal request from Yu for the door to open and show him what happened in his past may factor into being able to access these memories. The further back scenario able to be accessed is from Earth's prehistory where dinosaurs where alive in the world. Where they are able to be affected by what was alive at the time, Yu is caught up by a Pteranodon and brought towards a Tyrannosaur Rex. From a fall Yu experiences pain from the landing while in the memory.

With a lizard staring at them, Yu and Mika consider whether they can actually be seen. Memory delving allows Yu and Mika to see Mikaela not just alive, but existing in this prehistoric time before he would be found deceased in the later, but still ancient past setting of Greece. Yu and Mika would also see a shadowy orb like being emerge from the lizard. Further calories from Yu would allow Mika to draw upon his demon power for them both to reach past a mountain. It is there they would discover a seraph civilisation with many seraphs and shadowy eyeball entities.

In traversing the seraph civilisation within the prehistoric memory, Yu and Mika would learn further of the existence of the Tower of Babel and the Unrailed Elevator Technology that was available at this time. In finding Sika Madu and observing his conversation with Mikaela they would hear a homunculus referred to as "Yu". By concentrating, Yu finds he can read the indecipherable text Sika Madu was viewing. While Yu and Mika were watching this past exchange, unknown to them they were able to be seen by Yu the homunculus in the memory.