One of the pillars of Corp society and the single most important piece of civil infrastructure known to post-awakening mankind, Nanoblood is exactly that: Blood that is saturated with microscopic machines working in unison for various functions. Corp people as a result bleed silver, not red, and this also makes their eyes silver. And Corp citizens with a higher nanite count sometimes even have their veins shimmering under their skin, as heat generated from the nanites are dispersed as photons.
The science behind nanoblood is beyond any human; as it was originally a gift from GENECIA to interface with her chosen. However, administration of Nanoblood varies from culture to culture. On P4-11, Gaia - because it is a new colony, Genecia forbid Nanoblood injection into minors because the overall culture of the planet is not mature enough to deal with nanoblood heredity (and thus, dependence). The Aohu Accord outlines the hygiene and legal obligations of any nanoblood implementation into individuals.
The presence of nanoblood could integrate a millionfold capacities that can be construed as even superhuman - killing bad cells, removing waste and unhealthy elements from ingested food, prolonging of human life and so on. However most unaffiliated humans mistake that every Nanoblood user has these amazing traits. The nanoblood itself is simply a platform very much like a mobile phone in which numerous applications can be downloaded to extend its functionality.
The use of Nanoblood is both obligatory and permanent to the Corporate citizen system, in which all Corp belong to comprise of citizens of legal age possessing nanoblood. Each citizen may sell or buy shares in themselves and other individuals as if they were a corporate entity, with the entire decentralized framework residing with Genecia herself.