Substitute Shinigami

Substitute Shinigami
A Substitute Shinigami is someone who became Shinigami by obtaining another Shinigami's power, or by going through a much harder and riskier process to transform him/herself into one. Obtaining another Shinigami's power is done by thrusting his/her Zanpakutō into the person's chest who wants to obtain the power. However, the percentage of success is low. In the case of success, the person normally obtains around half of the Shinigami's power, and only temporarily.
his practice is forbidden by the Soul Society, as it can give birth to rogue Shinigami with great power, thereby it is only applied as a last resort measure.
In the case the individual borrowing the power being a Human, several difficulties arise. In order to be able to fight as a Shinigami, he has to leave his body and get into soul state, which can only be done if he is "killed" (at least put into clinical death) by the "skull symbol" of another Shinigami, or if he swallows a Soul Candy, forcing his soul out of his body. In the former case, his body needs to be taken care of until he finishes his job and re-enters it.
The other method of becoming a Shinigami is even riskier, and is only possible for individuals with spiritual power well above the average level. The only example so far is Ichigo Kurosaki. In the first step, his soul was forced out of his body and his Chain of Fate was cut. In the next step, he had to get accustomed to controlling his spiritual body confidently. In the third step, he was forced into a situation from where he can only escape by using Spiritual Energy. To be able to use it, he had to communicate with the spirit of his own Zanpakutō, who has been lying dormant in the depth of his soul up to this point, and find his own Spirit Thread. Had he not succeeded in his step, he would turn into a Hollow. Finally, he had to learn the name of his Zanpakutō and call it out, releasing its Shikai.
Despite the above-mentioned difficulties, there are known examples of successful and valuable Substitute Shinigami, as mentioned by captain Jūshirō Ukitake. These Shinigami, including Ichigo after the Ryoka Invasion of the Soul Society, receive a badge called the Seal of Approval. This item serves several functions. One is to identify the owner in the case he/she meets other Shinigami, another is to indicate if Hollows are nearby via an alarm sound. The alarm can only be heard by the owner, and the item itself is only visible to other spiritually aware beings, allowing the owner to keep it with him/herself all day long without attracting unwanted attention. The Seal of Approval can also fulfil the functions of the Shinigami "skull symbol", being able of forcing out spirits out of their bodies, which comes in handy in the case of a Hollow attack, when the Substitute Shinigami has to leave his/her body immediately. The Seal of Approval has a skull symbol similar to, but not identical to the one carried by regular Shinigami engraved on it.