Video game characters, particularly in Adventure Games and First Person Shooters, have the seemingly superhuman ability to carry incredible amounts of stuff with them at one time, usually an array of weapons along with the ammunition for each one. It doesn't limit their ability to run and jump and crawl through small spaces at all. What's more, when you see them during cutscenes in first-person games and third-person games, you can't see where they've stowed these things, even when they're wearing clothes that are more or less form-fitting. It seems they've put them away in the same realm where Hyperspace Mallets are kept.
In practice, a Hyperspace Arsenal serves to reduce the more annoying aspects of inventory management, removing the need to constantly shuffle stuff in and out of your backpack. Some games may choose to restrict inventory for balance reasons: It might upset the difficulty curve if the protagonist can carry around an infinite amount of healing items. This can be more realistic as in Halo's rule of no more than two weapons at once or still kind of exaggerated, as in many Adventure Games' "you can only carry twelve items"-type ruling. The result, more often than not, is the more annoying variety of Inventory Management Puzzle (and often leading to its own ridiculous situations — bazookas regularly take up as much space as gum wrappers, and in weapon-limited First Person Shooters you might be able to carry around a rocket launcher and a heavy machine gun, but lord forbid you try to carry around three pistols).
In fandom, this trope is often "justified" with the supposition that the Hyperspace Inventory is actually kept in the character's pants (which actually serves to answer exactly none of the objections to the trope). Some less-than-serious works, such as Space Quest, Simon the Sorcerer or Monkey Island, take this very literally.
The reverse occurs in many text adventures, where (primarily for design reasons) the player character could only carry a specific number of items (often five) at any one same time. Regardless of how large these items are.
One odd effect of the Hyperspace Arsenal is that characters may struggle to support an item that they have "taken out" or "equipped," and they may not be able to wear something at all if they're not strong enough — yet presumably they're carrying this very item around all the time. Put another way, as long as you can't see it, it weighs nothing. (This could mean that the equipment is too heavy to be feasible in battle, though, again, this doesn't explain how you're lugging around a suit of full plate armor you're too weak to wear, as it is actually harder to carry a suit of full plate than it is to wear it)
Another odd effect, usually found in Adventure and Role-Playing games, is an inventory limit on a single kind of item. The classic example is being able to carry 99 healing Potions and 99 Antidotes, but not 198 Potions or even 100. Some games have even more stringent limits, which sometimes are item specific, and oftentimes aren't internally consistent (you might be able to carry around 50 healing potions, but only 10 healing herbs, because herbs are a different item category).
Compare Extended Disarming, which often happens when a character is asked to empty out their hyperspace arsenal. Compare also Variable-Length Chain, where chains and whips can "stretch" to attack a far target without being long when unused.
Contrast Walking Armory, where the character is actually shown carrying all of their weapons on their body, and Limited Loadout, which is where there's a more (relatively) realistic limit to the number of weapons one can carry.
The MythBusters tested this trope out to see if carrying weapons would significantly slow down an actual person in Real Life; The answer was that an ordinary person would be significantly slowed down by lugging around extra gear, but a particularly well-built or athletic person (such as a professional MMA fighter) is able to pull it off, netting it a Plausible verdict.
- Fairy Tail: Ezra's 'Re-quip' magic is essentially this trope. She has a bunch of different magical armors and weapons (along with normal clothes) stashed in some magical storage space, and she can put on and remove them nigh-instantaneously like she was a video game character. It's an exceptionally useful form of magic, since it means she can adapt her magic to fit whatever threat she has to face, though if said armor is broken in battle, she can't use it until it's fixed.
- Batman: The Bat clan's utility belts are usually where all their gear is assumed to be held but sometimes there's just no possible way they had room for an item or the number of items they use in the things. This is especially prevalent when they substitute small streamlined canisters for the pouches like on Tim Drake's first Robin costume.
- Diabolik often wears a skintight suit when on the job, one so tight it's practically painted on him... And carries a pair of knives somewhere in this suit. And it's not the utility belt, that one he wears rarely but he always has the knives.
- Hetalia: Axis Powers fanfic Gankona, Unnachgiebig, Unità: Parodied several times. From clothes to books to Death Notes to flowers, the characters' backs can store them all.
"It's alright Italia-kun. I always bring spare cosplays with me." He reached into some sort of secret compartment behind his back, pulling out an identical outfit to the one the brunet was currently wearing. Seriously, how do anime characters have such an ability?Japan disappeared into a bathroom for a short amount of time before reappearing, now clad in a sharp black suit and tie with a white dress shirt and black pants, taking hexagonal glasses from his pocket—or wherever anime characters store all their stuff—before putting them on."Humph." The larger scoffed back. He then reached into the magical space all anime characters have, whipping out a book conveniently titled 'How to Catch a Runaway Italian'.Both reached into the magical space all anime characters have, extracting black notebooks—Japan's having unidentifiable symbols on its cover as Italy's had 'Death Note' clearly printed on it in gothic letters—before taking out pens and colored pencils as well, opening the pages before scrawling in them.Giggling, the auburn reached into the magical space all anime characters have, an exquisite bouquet of utmost grandeur popping out from behind his back. "Tada!"
- A Crown of Stars: Justified. Avalon Empire soldiers have a technique called “Holdout Pocket”. It is a little spatial fold tied to their personal space that they use to store weapons –among other things-.
Shinji:“Where did you get this?”
TJ:“Holdout Pocket technique. A little spatial fold tied to your personal space, good for keeping an emergency backup weapon or something handy. I also keep cold drinks in mine. It’s not a hard trick to learn. First year Weapon Theory stuff. I could probably teach you pretty quickly if you’ve got a gun or a knife you’d like to try it on.”
- Thousand Shinji:
- Asuka did not know how hers worked, but whenever she required a weapon it appeared on her hand, and it disappeared when she no longer needed it. She keeps as many weapons as she wants of all shapes and sizes, although she shows preference for axes.
- Unit 02 pulls weapons out of nothingness during its Bloodthirster transformation.
- The Truth and the Tempest, a Ranma ˝ fanfic, actually explains Akane's Hyperspace Mallet ability and expands it into a limited version of this: she's unknowingly been using the Zaimoku-ken (translated as "Timber Strike"), a ki technique that can fetch just about any wooden weapon as needed, such as a mallet, bokken or tonfa. Akane herself explains that she learned it when she found a scroll that mentioned the phrase "loyal hammer", but just assumed it was a hidden weapons technique like Mousse or other martial artists use until it was explained to her.
- Origins, a Mass Effect/Star Wars/Borderlands/Halo Massive Multiplayer Crossover uses Borderlands version of this as-is, but new rules are made for them. Water cannot be stored (it becomes toxic if you do). Items can be "half"-stored (Athena's rifle is broken in half when the Storage Deck's power fails and she's only pulled it part-way). Samantha Shepard discusses how much she enjoys exploiting the notion of such things, since she was used to her Limited Loadout.
- In Wonderful (Mazinja), whenever Taylor needs a weapon, it instantly appears on her hands.
- In Amazing Fantasy, the "ribs" of Boomerang's costume are actually storage units that store a wide variety of boomerangs while adding next to no bulk to his biker-style outfit.
- In Rabbit of the Moon, the Messengers are able to take things to and from the Hunter's Dream. Because of this, Bell can give them his weapons to lighten his load, and summon them to retrieve his weapons when he needs them. To those lacking the Insight to perceive the Messengers, he appears to be pulling them from thin air.
- The Legend of Zelda: Paradise Calling justified the games' use of this with a Sheikah scroll that Link keeps behind his shield, allowing him to store his bow and arrows among other things.
- Despicable Me: Gru can store just about anything in his jacket. Freeze ray, the disintegrator ray at the theme park, THE MOON.
- Ready Player One, being set mostly inside an MMO-style virtual world, generally has this trope in effect. However, it doesn't seem to apply to all items, because at one point Wade mentions using a magic spell to shrink his spaceship down to fit in his pocket.
- Blake's 7 had a tendency to this due to characters' tendency to wear very tight leather costumes or evening gowns, but Dayna became particularly notorious for her ability to produce large guns and bombs between shots without having had anywhere to stash them.
- Kamen Rider Gaim has a literal example of this with the title character's Super Mode Kiwami Arms, which can summon every other Armored Rider's weapons from thin air just by activating the lock-and-key mechanism that makes up his Transformation Trinket. This gives him access to: two different swords, a flail, kunai, a lance, a mace, a handgun, wind and fire wheels, a shield, two kinds of spears, a hammer, paired serrated swords, bows, and his personal BFG-slash-BFSnote . And if that wasn't enough, he can use telekinesis to fling the summoned weapons at his enemies.
- LazyTown: Sportacus' backpack can transform into a gyrocopter and contains far more bats, rackets, balls and other sports equipment than should be able to fit into it.
- The Mythbusters test of the trope occurred during their "Video Game Special" and involved an FPS-style combat course modeled after Doom. Adam and Jamie ran the course once discarding each weapon as they picked up a new one, then did it again keeping each new piece of equipment as they found it until they were carrying an 80-pound load. Both struggled visibly during the second run, taking nearly twice as long to complete the course as they did the first time through. Professional MMA fighter Brendan Schaub, on the other hand, made it through the course just as fast with the full load as he did unencumbered — not only that, but in his enthusiasm he forgot to actually use the backpack to store any of the items he was carrying, and still finished the course faster encumbered than either Adam or Jamie managed in their control runs, leading to the "Plausible" verdict.
- Zig-Zagging Trope in Dungeons & Dragons. While characters have a weight limit based on Strength (and lose mobility if they go over this limit), that's the only concession to reality with regards to what someone can carry on their person. For example, any Fighter worth his salt would be lugging around a small armory's worth of weapons and ammunition in order to deal with creatures who only take damage under certain circumstances. However, with bags of holding and portable holes, this trope can be invoked literally.
- While GURPS generally takes a realistic approach to equipment and encumberance, characters with the Gizmo advantage can specify 1-3 times per game that they just happen to have exactly what they need on them, as long as it's small, portable, and something they could reasonably have (including pocket-sized inventions in the case of a Gadgeteer Genius).
- Only War mostly averts it with a carry limit calculated from the character's combined Strength and Toughness plus some can be carried by the comrade. They typically sum to more or less realistic numbers. And this being Warhammer 40,000, many weapons are incredibly heavy.
- While the chart for this goes up to two and a quarter metric tonnes, this requires stats completely unattainable to the player (both at 100, virtually impossible to get them past 75).
- Played straight with a number of minor items considered weightless. Weightless items are either things genuinely so small their weight would be negligible — like an exhaustively named pen — or things that losing capacity on would be a pain, such as most of the Universal Standard Kit, a rather large collection of fluff-relevant but gameplay-useless stuff invariably supplied to all players.
- Princess: The Hopeful: A number of Charms give a Princess various weapons, tools, or other items (collectively known as Regalia) that she can manifest while Transformed. A Princess can choose which pieces of Regalia she manifests when she Transforms and can dismiss or manifest a specific piece of her Regalia with a few moments of concentration, allowing a high-level Princess to have literally dozens of pieces of equipment at her disposal without actually having to carry them around.
- A Beginner's Guide to the End of the Universe: Items stored in the Everyman's inventory cease to physically occupy space, and don't burden him down despite often being quite heavy when taken out.
- Flipside: Justified thanks to the ready availability of magic and magic items in the setting. Maytag's ability to produce a bewildering variety of random objects out of thin air is eventually explained as coming from a Bag of Holding purse that places a Summon to Hand enchantment on its contents.
- El Goonish Shive: Susan's summoning spell appears like this, but she's actually just summoning magical copies of the contents of a physical box.
- Kaeloo: Mr. Cat has an arsenal of weapons which he can randomly pull out at any time, which consists mostly of bazookas, guns, chainsaws, knives, mallets and others. Lampshaded in one episode where he says he is carrying a bazooka, a chainsaw and a cluster bomb, while his hands are completely empty.