Essentially, the ability to open and close doors. Ooooh, scary. But picture this. The user in question seals you inside a door to another dimension for centuries, or perhaps opens a door to the infernal planes and fishes out a few monsters. Still think so?
This power is commonly tied to a Cool Key. Thus, the favored weapon of this user is usually a giant vaguely (or not so vaguely) key-shaped staff. It is favored by exorcists since it is a quick way to deal with fearsome creatures without converting to the religion. All you need is to find a handy door to lock all your worst nightmares away behind. Just better hope they don't decide to team up to rush the door.
In its most basic form, this is basically a combination of Barrier Warrior and Thinking Up Portals. That is, you can open/close doors to anywhere (and open any doors), or send incoming attacks into another place. But this is very much a Semantic Superpower (in fact, the ability to open doors is currently the quote for the page), so other applications of this power can be made.
Because you can open any door, there might be some overlap with the various Elemental Powers. Most obviously is Space/Time in the form of dimensional travel, but you could conceivably use fire magic by opening a tiny hole into a volcano or something, or water by opening a hole into the middle of an ocean. If the definition of this power is vague enough, this becomes a Swiss-Army Superpower.
Not to be confused with an Open-and-Shut Case.
- Cardcaptor Sakura, the title character uses a key as a tool to lock away or unlock spirits. The first episode she unseals them all by accident.
- The Lock Card also has the ability to seal anything.
- Doraemon staple gadget "The Anywhere Door" is just that, a door that takes you to a place of your choosing. You have to be pretty specific about where you're headed, though. (Saying "I wanna go high up", for example, opens a door in midair.)
- Natsume's Book of Friends has a kid who ancestor sealed a bunch of monsters away in a book. He decides to release them.
- CP9 agent Blueno of One Piece got this power from the "Door Door Fruit". He can use it to pass through any wall or obstacle, enter a pocket dimension by making a door in the air and even use it in combat by turning someone's face into a revolving door and spinning it.
- In Hunter × Hunter, Knov has a limited version of this as his power: He can create a door anywhere that will take him to a special room in another dimension of his own creation that cannot be detected or accessed without him acting on it. Consequently, Knov can create doors out of this room to anywhere he wants.
- The obscure Marvel Comics character Ariel had the power to open any door and make it connect to any other door. She claimed that anyone could do this "if they know hyperspacial geometry and have the right kind of hands."
- In The Matrix, The Keymaker is a program able to access the key to anything, from locks to motorbike ignition switches.
- The Adjustment Bureau: The men of the Adjustment Bureau have the power to open any door to any other door, allowing them to close in on any target rather swiftly. This ability is not innate to them but provided by their 1950s-style hats; one of them temporarily gives his hat to the hero so he can beat them at their own game.
- Abhorsen in the Old Kingdom series can open gates to and between the nine levels of Death, and can also bind away spirits or undead using bells. In fact, their magical alphabet itself is constructed as a result of a major seal.
- In Labyrinths of Echo, Numminorikh Kuta learned the art of finding and opening any kind of doors from his mother, who was the Master of Doorways for an ancient Magical Society. Also, Max can use doors of any kind to access the Corridor Between Worlds, and suffers major Power Incontinence in the final tome.
- "The Lost Gate" of the Mither Mage series by Orson Scott Card has the main character seemingly having no power. He later turns out to be a Gatekeeper.
- In Monday Begins on Saturday, a pair of Maxwell's demons work in the Extranormal Institute as the doorkeepers.
- In Neverwhere, Door is a member of the family Portico, who all have this ability, and are highly regarded because of it. They live in a series of rooms that aren't physically accessible by ordinary means. The ability — now that the rest of her family is dead — makes her a MacGuffin Super Person for the plot.
- The Alohomora spell in Harry Potter (and its locking counterpart, Colloportus), although (understandably, in a world where a bright first-year student can unlock any ordinary door) there are magical locks which are able to resist it.
- Evan Matthieu, in Pact, is the ghost of a child who becomes a wizard's Familiar, in the process gaining several powerful abilities from other ghosts in his vicinity. Since this vicinity was a police station, these abilities include a Five-Finger Discount and the ability to open doors by touching them.
- One of the main uses of The Subtle Knife, which can cut through anything, including the walls between worlds.
- Multiple villains on Angel have been able to open interdimensional portals. Sahjahn was able to open a door to any dimension. Fred's professor in Supersymmetry was a magic user with a penchant for exiling students who threatened to surpass him to other worlds. Illyria was also shown to be capable of opening interdimensional portals before Wesley de-powered her.
- Kamen Rider Drive: One of the Monsters of the Week is the Open Roidmude, which has the power to telekinetically open things like doors, boxes, and the like. It ends up getting on Drive's nerves quite a bit, since it can shut down his Door Gunnote and Justice Hunter powersnote .
- Dungeons & Dragons has the gate spell. Sure, you can head to other dimensions. Or you can summon creatures from them (including elementals, enabling fire effects). Or you can suck/push creatures into other dimensions. Or you can block incoming spells. Or you can create two portals in close proximity, and mimic spell-turning (later versions likely patched this detail).
- On a much less impressive scale, the Knock and Hold Portal spells do Exactly What It Says on the Tin.
- The Lore of Portals of the House of Neberu in Demon: The Fallen is a set of magical/divine abilities revolving around opening and closing doors of any kind.
- Obviously, the stock power of the Keyblades in Kingdom Hearts series. Both are used to great effect over the course of the series.
- Touhou: Yukari Yakumo's ill-defined but tremendously game-breaking power is over boundaries, which she can open and close at will. Usually this manifests as elongated Portal-style openings in reality (called gaps), but she can also manipulate conceptual boundaries, like the border of Gensokyo or the boundary between life and death.
- The world of Fire Emblem Heroes centers around a war between two kingdoms with this power divided among them; the Kingdom of Askr has the power to open portals to other worlds, while the Kingdom of Embla has the power to close portals to other worlds.
- Will from W.I.T.C.H. can not only call up dimensional portals, but she has the ability the sync up the rest of the team's powers to allow their transformation.
- Maxwell's demon (in thermodynamics) is a hypothetical entity whose only powers is to open and close doors.
- The Great Grimoire of Honorius makes special mention of the demon Surgat as "he who opens all locks", and is the only demon the Pope in question could not shake. This coming from a guy who intentionally summoned demons explicitly to banish them back to hell as a workout for facing Satan.
- Fission and Fusion operate off the process of joining or splitting bonds, so yes, this can be very powerful.