Realm Exclusive Effect

People who live in a world much like ours where they are just average with nothing supernatural or extraordinary. While in another world, they have superpowers, and when coming back to their world, their powers are usually inaccessible. The setting usually has two worlds that people can go from one to another, such as a portal, teleportation, a mystical artifact, or other means.

An staple trope of the Isekai genre,

Anime and Manga

 * Yumeria has a dreamworld called Moera where the character gains different outfits, powers, and weapons. The main character can also give the others in Moera a boost in power.
 * Averted in Fairy Tail where the characters are brought to Edolas and can't use magic unless they use certain equipment. This is solved when they swallow a crystal which allows them to use magic normally.
 * Yumeji, from Dream Eater Merry, has an ability called Lucid Gear that can only be used in a Daydream.
 * Played with in the manga Isekai Ojisan: when the titular character was dragged to a fantasy world, he didn't have any special powers there, but he was able to learn the local magic. Then he is returned to the modern world 17 years later, he still has the knowledge and can use magic.

Comic Books

 * The manfra, Dreamland, have people known as Traveler who gains access to the titular setting by facing their phobia and gaining a power related to it.
 * Amethyst, Princess of Gemworld in the original series featured Amy Winston, a normal teenage girl who travels to the magic-ruled Gemworld and transforms into Princess Amethyst. While on Earth, she's a normal girl without any powers, on Gemworld, she possesses the magical powers of the House of Amethyst.

Literature

 * In The Chronicles of Narnia: The Pevensies experience this trope. In the real world, they're just British kids living in the 1940s. But in Narnia, they're powerful kings and queens.
 * Also, to top it all off their reputation in Narnia is similar to King Arthur's.

Video Games

 * Tokyo Xanadu has the Eclipse, which is an overlap of reality with the Spirit World where certain people can use armaments called Soul Devices that can be used against creatures called Greed.
 * Subverted in Persona 4 and 5 where the characters can summon their Personas while in the TV World and Metaverse, respectively. The characters within the setting believe that they can only summon them in the alternate dimensions. They can still summon them, but they would need to under heavy duress or the use of an evoker.
 * The Longest Journey has the two worlds of Stark and Arcadia that each have science and magic, respectively. A shifter can go between the two and have access to magic while in Arcadia. Stark favors science and technology compared to the use of magic in the Arcadia.
 * In Viewtiful Joe, the V-Watch cannot be used in the Real World and only in Movieland. To circumvent this limitation is through the use of being filmed by a V-Cam to transform with it.

Web Comics

 * In the Layers webtoon, certain teenagers can teleport to another world called Layer and have the powers such as telekinesis. Once someone becomes an adult, they lose the ability called Transfer that allows transportation to it.
 * Her Summon webtoon has a Summoner from another world summons Jin-Kyung from modern-day South Korea. While summoned, he gains magical powers through the use of objects brought with him. He uses these mundane items as a conduit for spells while the item gets used up as a battery would become dead and an insecticide gets emptied. When he is teleported back, he loses magic even when he tries a spell with an item that hasn't been used up.

Western Animation

 * Midnight Patrol: Adventures in the Dream Zone has the group and children and their dog are normal until they each have special powers while in the Dream Zone
 * Twelve Forever has the three protagonists who can teleport themselves to Endless Island where each has a unique power. Twelve get superhuman strength, Esther can create whips of light and transport made out the same material, and Todd is a shapeshifter.