The Cursed Seal of Yellow Spring is a unique Cursed Seal even among Orochimaru's various juinjutsu. It was developed by Orochimaru following the Fourth Shinobi World War, based on the new data he had gained from experimenting on Jūgo, as well as the Shinju and Hashirama Senju's own Sage Mode. While it wasn't a replica, per-say, it appeared to emulate the effects of Jūgo's own Sage Transformation, at least on the animal samples that he used them on. Ichimu was the first human that the technique had been used on, and surprisingly, it was a success. Ichimu had been able to sustain his own chakra levels by mediating them with the influx of natural energy in his body, therefore causing him to become a passive user of Senjutsu; albeit inadvertent.