Micro Cosmos

Micro Cosmos is a mysterious term referenced by Kumokawa Seria in Shinyaku Toaru Majutsu no Index.

Principles
After losing her eye, Kumokawa Seria requested Kaizumi Tsugutoshi to prepare the parts of her divided into the Micro Cosmos, and eight hours later, a new eye had been transplanted and she had gotten used to it. This indicates that it contains fresh body parts of hers, and the reason why Seria was unperturbed by Tsuchimikado plucking her eye out.

With how the kanji may mean "Bottling Plant", Micro Cosmos is most likely a facility or a system that keeps spare body parts, though this is just plain speculation.

Agitate Halation Arc
After Kumokawa Seria believed she defeated Tsuchimikado Motoharu after he took out her eye, she requested Kaizumi Tsugutoshi to prepare the parts of her divided into the Micro Cosmos. Eight hours later, after the events of the Agitate Halation Project, she had a successful eye transplant and had already gotten used to it to the point that she didn't feel like there is something in her eye anymore.

Coronzon Arc
Kumokawa Seria's loss of an eye and repair using one of the spare parts she had preserved elsewhere (i.e. the Micro Cosmos) was known to Mina Mathers and referred to in the narration during her discussion with Heaven Canceller about the methods needed to give Lilith Crowley a physical body.