Memoria

Memoria is a pseudo-world made of people's memories. It can be accessed from Archivio Space by the Sky Priestess.

Because Memoria is based on somebody's memories of a given location, it is usually slightly different from the real version. This applies even to things that the originator recognizes is incorrect, and is not corrected even when they point it out.

Memoria is formed based on Mukashikku Cubes, which store the Mukashikku Record of people's memories, and is physically built out of Memoria Cubes. However, the extraction of Mukashikku Cubes removes the related memories and abilities from that life form's mind, significantly weakening them and causing them to forget details (though, notably, general information is retained). To recover this information, the individual must travel through the Memoria, reliving their experiences (albeit altered).

When a Memoria is generated, the originator of the memory is removed from its world, allowing them to travel inside and take their place. However, due to the intensity of memories, memories of people appearing in Memoria are much more powerful than they were in the real world.

Though unexplained, it has also been shown that memories of people inside a Memoria can resonate with the Sky Priestess' Mukashikku Cubes, forming memories of people from their own past and incorporating them into the current Memoria. This seems to occur in times of heightened emotion, and the newly formed being dissipates when their originator calms down.

Hysteria
Hysteria (ヒスタリア) are Frayed Memories (記憶のほつれ) in a Memoria. They are particularly distorted bits of memory, causing rips in the world of Memoria. To resolve them, the originators must enter the rips and correct issues plagueing them. However, not all originators can enter the Hysteria; some will simply walk through the tear in space without entering it.

If somebody enters a Hysteria and is unable to solve the problem within it, they are incapable of leaving, becoming permanently trapped inside.

Due to being so heavily distorted, they only slightly resemble the actual memories of the location, and merge memories of multiple events. They also only contain a small area, which is limited by the bounds of the unclear memory. Notably, Hysteria reflect the Memoria world without any changes made by the originators.

Archivio Space
Archivio Space is the connecting point between Memoria and the real world, and is where somebody's body remains when they enter Memoria. It is made of elements generated by the Tower of Heaven, and is used to store Mukashikku Cubes.

Mukashikku Cubes
Mukashikku Cubes (ムカシックキューブ) are the crystallized form of Mukashikku Records (ムカシックレコード), which represent a life form's memories. Mukashikku Cubes can be extracted from a life form by the Sky Priestess, and only hold their shape within a 10 km range of the Tower of Heaven on Waford.

In the English version of One Piece Odyssey, they're called Olassic Cubes and Olassic Records respectively.

One Piece Odyssey
After having their memories removed by Lim, the Straw Hat Pirates traveled through their past adventures in Memoria.