Key

A key is an object designed to open or close a lock. Keys appeared as items in several games from the Mega Man franchise with different shapes and purposes, usually as an item required to open a locked door to access a new area.

A typical key is a small piece of metal which slides into the keyway of the lock to open. Card keys are flat, rectangular cards that store a physical or digital signature, which can be used to disengage a card key lock. In the Mega Man Battle Network series, passcodes serve a similar purpose in the Cyberworld by giving access to an area.

Mega Man Zero 4
ZeroXorZ can use the Zero Knuckle on the NicosCrabC in the Hibernation Chamber to take its Card Key, which opens a door that leads to a Sub Tank. It is immediately destroyed when used to attack an enemy, so the player must keep it until the locked door.

Mega Man ZX
While performing missions to the Guardians, Vent / Aile obtain card keys that grant them access to new areas.

The game also contains one unused card key:

Mega Man ZX Advent
Grey / Ashe obtain two card keys to open doors in the Hunter's Camp. The game also contains an initialization key to activate a transerver. In a sidequest, the Hunter Richard lends a Firing Range Key to let the player fight an horde of.

Mega Man Legends
Keys are Special Items used by Mega Man Volnutt to open locks.

Mega Man Legends 2
Hangekal

The Misadventures of Tron Bonne
Card keys are used by the Servbots in the Shala-Kun Ruins.

Mega Man Star Force

 * KeyMan
 * Andromeda Key

Mega Man Star Force 2
Mega Man must obtain the Whazzap Key (shortened WhzzpKey in-game, ナンスカへのカギ, "Key to Nanska" in Japan) to open the door to Whazzap.

Other media
A card key appeared in MegaMan NT Warrior.

The Short Circuits from Mega Man #49 has a Robot Master named I Can't Find My Keys, Man!. As his name implies, he can't find his keys.