Not much is known about the Tama. The Tama is also referred to as Sekirei soul, Sekirei core or Sekirei spirit. Basically, it is the core/nucleus which let Sekirei live and use their powers, so in essence the life of a Sekirei itself, a Sekirei who lost its Tama ceases to function. The core is created from a material that goes together with the Jinki, by using these, you can turn on and off the core and freely control all of the Sekirei.The Tama can be placed into other bodies as done with the Tama of #08 Yume which she gave to #88 Musubi. A statement of Homura also indicates that the Tama can change bodies. He once thought about requesting another body from Sahashi Takami.