The user's very bloodstream is primed with nanites, which can often enhance the user's physical performance and/or possibly allow the user to manifest special abilities, among other things. Simply having nanobots in the user's bloodstream makes them superhuman since it's beyond normal or peak human capacity.
Creed Diskenth (Black Cat) possesses the God's Breath nano-machines within his body, regenerating even fatal wounds in seconds and maintaining his youth, but cannot repair damage to the brain.
Lex Luthor (DC Comics) was inserted a payload of nano-tech copy by Brainiac, who laid dormant to regain strength. As Brainiac got stronger, it also strengthened Luthor's body, curing him of his Kryptonite-induced cancer and giving him superhuman strength, and the two eventually agreed to unite into one almighty being.
Nathan Christopher Summers (Marvel Comics) is a T.O. infected mutant being with a nanomolecular infused symbiosis sporting billions to trillions of microscopic A.I. computers firing off in his mind and body.
Senator Armstrong (Metal Gear Rising: Revengeance) has nanites within his body.
Golden Darkness (To Love-Ru) possesses nano-machines in her body, allowing her to change her body parts into weapons for combat.
having been infused with an A.I driven nanoactive plasma, Bloodshot (Valiant Comics) boasts many incredulous abilities. Key among which is his uncanny capacity for self-repair.
Hayden Tenno (Dark Sector) afflicted with the technocyte virus was steadily flooded with transorganic nanotechnology steadily enhanced and sharpened his physiological capabilities.
The body of a former Geomancer was used by P.R.S to give rise to the ultimate nanite fluid empowered killing machine, Deathmate (Valiant Entertainment).
Rex Salazar (Generator Rex) is an in incredibly apt user of various nanotech implants flowing in his system.