In their studies of Waveworn Phenomena, scientists discovered "Tacetite" — a substance that can permanently hold Remnant Energy. The Tacetite can be made into potent weapons for Resonators to combat Tacet Discords. Transdimensional spaces where Remnant Energy is abundant are known as the Sonoro Spheres.
From the original Chinese text:
回音 一种纯净，完整的频率能量形态，其记录的信息能够超越时空以某种形式稳定存在。 经研究发现，海蚀现象的产物「黑石」可以完整封存承载「回音」能量。加以改造，可作为共鸣者可使用的强力能源武器，对残象造成有效伤害。 其富集形成的超自然空间区域，学界称之为索诺拉。
Remnant is a pure, complete form of frequency energy, whose recorded information can exist in a stable form beyond time and space.
Research has found that the product of the Waveworn Phenomena, the Tacetite can completely seal and carry the energy of Remnant. With modification, it can be used as a powerful energy weapon by resonators to effectively damage Tacet Discords.
The supernatural spatial regions formed by its accumulation are referred to as Sonoro by academics.
Thanks to the description of the Reverberation, we know that when the Waveworn Phenomenon occurred, matter, information, and energy are all reduced to vibrating frequencies. The residual, ever-decaying frequency energy that remains afterward is called "Reverberations”.
We might therefore infer that Remnant, a pure form of frequency energy, came into existence because of the Waveworn Phenomena, and that it is itself, decaying to originate the Reverberation, as it is also mentioned in the Waveworn Residues 210 Waveworn Residue 210
The Remnant is a pure and complete information that remained elusive and intangible and exhibits an astonishing balance.
Despite their advanced technology, scientists could not capture or analyze this powerful force but only its decayed residues. They seek to create Artificial Sonoro Spheres in order to extract pure Remnant Energy and to eliminate the abnormal impure frequencies within as much as possible.
As this substance is essential for many advanced fields, the world has imposed the strictest trade restrictions on it.
Various events across space and time from every dimension are recorded in the form of Remnant Energy. It sometimes gives rise to memory manifestations of sentient beings. This because Remnant Energy has the intrinsic property of interacting with external frequencies, merging and changing structure, giving shape to new realities that are extremely connected to the frequencies with which it came into contact. This characteristic can be observed through the Sonoro Sphere and the Retroact Rain, both Waveworn Phenomena formed by Remnant Energy.
CBT2 Reverberation description: According to research observations, once the Remnant decays, it will become a Reverberation, and this process is irreversible.
In the description during CBT2, it was even mentioned that the process was irreversible. To date we have no other descriptions or facts to prove otherwise, so it may indeed be an irreversible process, as indeed the actual real properties of sound also prove, however, it is to be evaluated since it is a part that has been removed.