Soul Shadow is not a monster per-se but rather an illusion of an apparition similar in appearance to Nephrite even though some specify that it is itself a part of him . Similar to the youma Leo the Lion, Soul Shadow was not involved in any energy-absorbing plots but was used by its master, Nephrite to rob the visiting Princess Diamond from the Diamond Kingdom, the royal treasure she is set to inherit at a reception inside the Diamond Kingdom embassy. Both Luna and Queen Beryl speculated that the royal treasure could be the legendary Imperium Silver Crystal with Luna adding that Princess Dia(mond) may be the Moon Princess that she is searching for. Consequently, both Luna and Queen Beryl of them assigned their subordinates to look into this matter. Nephrite, who snatches this assignment from Zoisite, notices Naru Osaka (Molly Baker) inside the embassy.
Given that her feelings for his alter ego (Masato Sanjouin [Maxfield Stanton]) would make her vulnerable, Nephrite flattered her before implanting his youma inside of her and taking complete control of her mind. Nephrite then used her as a "middleman" to enter the princess's quarters and "pass" the youma onto her, so the latter could steal the treasure. The power of the youma was controlled by the concentration of Nephrite. What was supposed to be an easy assignment was complicated by Usagi (Serena) Tsukino (who snuck into the embassy with her disguise pen), where she was alerted by Luna of the theft of the treasure and in her botched attempt at stopping the possessed princess from handing it to Nephrite, slips and falls from the balcony. Tuxedo Mask who catches her by the hand is bumped from behind by the possessed princess. "He doesn't fall, but Luna sees what is happening and attacks the princess". Consequently, Nephrite's concentration in the youma was disrupted by the intervention of Sailor Mars and Sailor Mercury who prevent Nephrite from finishing off Tuxedo Mask and Usagi (Serena) Tsukino.
When he retreats to block away from the embassy, Nephrite uses his concentration via his evil crest to reawaken his youma who was still inside the body of Princess Diamond. The possessed Princess Diamond was able to use the power of the youma to blast dark energy at the guests inside the embassy making the fall to the ground unconscious as she again uses the power of the youma to leap off the embassy balcony and float to the ground. “She tries again to deliver the treasure to Nephrite, but Sailor Mars exorcises” the youma from the possessed Princess Dia(mond) using her anti evil scroll attack. The youma floats out of her body and attacks Sailor Mars, Sailor Mercury and Sailor Moon with the a blast of dark energy. Sailor Mercury uses her Sabão Spray (Mercury Bubbles) attack against the dark energy attack causing it to stop. This gave Sailor Moon the opportunity to In the manga. In Act 4 (Kamenfutoukai - Masquerade), Soul Shadow was actually a female youma disguised as an interpreter for Princess Dia(mond). The youma is destroyed by Sailor Moon's "Moon Twilight Flash" attack.
- Soul Shadow's death can be seen in the dub of the opening sequence of Sailor Moon.