Modified Soul

, more commonly referred to as Mod-Souls, are artificial souls designed to enhance regular Human physiology, making them capable of battling Hollows equally. The technology was created by Ōko Yushima.

Overview
Modified souls were created through Project, in an attempt to even the gap between Shinigami and Hollows, as Hollows generally outnumber Shinigami. The Mod-Souls created varied in their abilities and can be defined by different types. For example, one Mod-Soul may be able to run many times faster than a regular Human while another may be many times stronger than normal. Kon, the Mod-Soul accidentally ending up in Ichigo's possession, has enhanced leg-strength, which makes him a Underpod (部下強化型 (アンダーポッド), Andāpoddo; Japanese for "Lower Part-Strengthened Form") type of Mod-Soul.

The Mod-Souls, just like regular artificial souls, are condensed into tiny, candy-like orbs. However, their originally intended purpose was to be placed into corpses to achieve their function as soldiers to combat Hollows. To fit with this purpose, they are also more independent than regular artificial souls.

The Mod-Souls were exterminated after the experiment was halted due to ethical reasons, since they were intended to be used to reanimate Human corpses to be used as weapons against Hollows. Kon was somehow mixed into a batch of Gikongan that contained normal artificial souls and shipped to Kisuke Urahara's shop, where Rukia and Ichigo obtained him and unknowingly let him loose. Despite a standing order to dispose of all modified souls, they kept Kon and placed him into the body of a lion plushie. Rukia and Ichigo use Kon to possess Ichigo's body when his soul is expelled from his body to fight as a Shinigami.

Additionally, Urahara created three additional Mod-Souls (Ririn, Kurōdo, and Noba) and installed them with Bount detectors.

Inaba's Cloned Modsouls
Ōko Yushima created the Mod-Souls and hid the technology within the Dangai when Project Spearhead was discontinued. He created two Mod-Souls from himself, Nozomi Kujō and Kagerōza Inaba, transferring his memories to Inaba as he did so, leaving himself in a catatonic state. Years later, Inaba researches the Dangai and finds the technology in order to use it in his revolution. He begins to take samples from highly ranked Shinigami as they travel through the Dangai. He uses these samples to combine them with his Mod-Soul technology to create enhanced clones of the Shinigami. He then places these clones into Reigai so that they can infiltrate the Gotei 13 in order to put his plans into motion. He places a bracelet on his Reigai to limit the spiritual power of the Mod-Souls, which can be taken off at anytime to unleash their full power.

The enhancements can come in several forms depending on the Shinigami's powers and the clone's appearance can also be modified if the physical profile of the original Shinigami is undesirable. Also, these Mod-Souls do not die if their Reigai is defeated, but only if they are destroyed in the Red Pill form that they reside in while not within the Reigai. These Mod-Souls are also unique in that their eyes have violet flashes in them while energized that can help distinguish the clone from the original.

Known Mod Souls
(† = confirmed death)