
Keiji was killed by Donovan Hock for his heavily-encrypted graybox. Only two individuals are known to have grayboxes, partners Kasumi Goto and the late Keiji Okuda. When a graybox is accessed by a specialized reader, the collection of memories contained within appear as snapshots, while the memory being viewed is played as a video.

As such, its usage was ultimately restricted to people who sorely needed eidetic memories, like researchers and intragalactic spies.

Launched by Synthetic Insights in 2160 CE and originally developed to help treat Alzheimer's disease, it was determined that its implant procedure has dangerous side-effects: should the graybox either need to be removed for maintenance purposes or if it developed software bugs, extensive brain damage would occur. A graybox is, essentially, a collection of snapshots of a person's memories.
