Implanted Armor

The protection that will always be with you. Truly last-chance armor.

May be an obvious carapace, may be subdermal. Of course, in the latter case, rather than being prevented, an injury only becomes superficial, and the beneficiary presumably still feels it… but it's better to lose some skin than liver. Usually it can't be too solid, so as not to restrict the movement too much, but it's better than nothing. Likely to be differentiated (as all practical armor for as long as there is armor) - sometimes limited to vital organs only.

Examples of Implanted Armor include:

Comic Books

Wolverine has had his skeleton treated with super-metal adamantium (The how and why Depending on the Writer and what version of Wolverine). For normal people this would be deadly as adamantium is toxic, but Wolverine can survive it with his Healing Factor.

Myths and Legends

Mahabharata, of all books. Karna has magical armor as a gift from his real father (the Sun god). As such, when he finally chose to remove it, he had to cut it out.

Tabletop Games

Warhammer 40,000: some cyborgized humans have this; warriors of Mechanicus have integrated carapaces; Orks sometimes bolt armor plating to their bodies (they are tough like this).
- Warhammer 40,000 Roleplay has both Cranial and Subskin Armour as separate implants. Also, general augmentation represented by Machine(X) trait or The Flesh is Weak (X) talent adds Armour Points. Cybernetic constructs have a significant amount of the latter, and often also integral armoured plating on top. Of the aliens, the Rak'Gol (at least, those encountered by humans) commonly have implanted plates (see Rak'Gol Marauder — common foot soldier, Rak'Gol Abomination — leader).
Among the many cybermods available in Shadowrun are Dermal Plating, Dermal Sheathing, Orthoskin, and other varieties of implanted armor.
Similarly, Cyberpunk 2020 from R. Talsorian Games offers the Skin Weave cyber mod, which makes the skin of the recipient's torso equivalent to light body armor, and Body Plating, which is just what it sounds like -- bolting armor plates onto the character's body.
Stars Without Number (Revised Edition) has Dermal Armor implant; it's as good as common TL4 combat armor, but 20× more expensive and gives constant 2 points of System Strain (most inflict 1), that limits amount of healing via psionic powers or most drugs per day.

Video Games

Both Fallout 2 and Fallout: New Vegas offer this as an inplant. In Fallout 2 the player must complete a sidequest to find the details for the procedure, find a suit of combat armor (which is a bit harder than it sounds as the game has many variants of the armor and only the most basic of of them works) and, if two layers are added, the surgical scars will permanently lower the player's charisma. In New Vegas the implant can simply be purchased with no negatives aside from taking an implant slot.

Web Comics

Schlock Mercenary has it as uncommon, but less than exotic augmentation, used in military (obviously) and some professional sports. Usually limited to the brain-case, since medical nanomachines can reconstruct the rest of one's body later. Presumably, various "soldier boosts" include a lesser version of this, since other bones are significantly reinforced; Laz-R-Us boosts include "runt Super Soldier" mode, which includes visible armor plating of the body. Of the named characters, John Der Trihs was reduced to head in a jar many times, but survived - thanks to the whole skull being replaced with armor. Among the non-humans, Ezraene Venombrook (she introduces herself as "Daggermother, Urtheep Industries Hot Mess Response Team", so it's professional too) has heavily reinforced skull.