The Soul Blade is a powerful technomagical ability that allows a knight to supercharge their mech beyond its normal operating limits at the cost of their own soul. This is achieved by permanently damaging the Sheath, a cybernetic implant in the pilot's skull that keeps a permanent record of their memories to be uploaded to Avalon on their death. The destruction of the Sheath precludes the knight's consciousness from being uploaded to the Unseelie Court, a realm within Avalon where the souls of deceased knights reside. Only a select few knights are deemed disciplined and stable enough to wield this dangerous tool.
The destruction of a soul is a heavy price to pay, so the use of the Soul Blade is strictly regulated by the Order of the Sundered Heart. Any deployment of the Soul Blade must be approved beforehand by the Sundered Heart, or a tribunal will be called to determine whether its use was justified. Those knights who are deemed worthy of learning the Soul Blade are inducted into the Order of the Sheathed Soul. This is an additional responsibility, not a replacement for the knight's current order.
If a member of the Sheathed Soul is forced to use their training with the Soul Blade, they will be admitted into the smallest order in the Starlit Court: the Order of the Unsheathed Soul. Members of the Unsheathed Soul are unable to be uploaded to the Unseelie Court, a realm where the souls of deceased knights reside. Instead, their physical bodies are interred in elaborate sarcophagi in the Mausoleum of the Soulless, located on the Island Sanctuary at the center of the Churning Sea on the capstone of Sihi.
Fortunately, use of the Soul Blade is incredibly rare, with only six members of the Unsheathed Soul having been interred in the Mausoleum. This is a testament to the strict regulations and honor code upheld by the knights of the Starlit Court, as even a single knight's sacrifice is considered a terrible price to pay for the continued safety of the Court.
Myths About the Soul Blade
According to legend, the High King was the first to make use of the Soul Blade, founding the Order of the Unsheathed Soul. The details of this event are lost to history, with various versions placing the High King on different worlds and at different times. It is thought that this is why the High King was not able to be uploaded to the Unseelie Court and why The Lady had to lead him to enlightenment and his eventual ascendance to Avalon.