Mewtu, known in English as Mewtwo, is a legendary Psychic-type Pokémon created through genetic manipulation as a clone of the ancient Pokémon Mew. In the television special Pokémon: Mewtwo Returns, which is a direct sequel to the first Pokémon theatrical film, Mewtwo has retreated to a secluded island in the middle of a pure lake atop Mount Quena in the Johto region. It has made this remote sanctuary its home, living alongside the cloned Pokémon it created from the originals it encountered during its first confrontation with humans. Mewtwo's background is defined by its unnatural origin: it was brought into existence by scientists working for Team Rocket, who sought to engineer the ultimate battle Pokémon. This origin left Mewtwo with a deep sense of isolation, confusion about its place in the world, and a fundamental distrust of humanity.

In terms of personality, Mewtwo is introspective, brooding, and emotionally complex. It struggles with existential questions about identity and purpose, often expressing doubt about whether it—and the other cloned Pokémon—truly deserve to exist as equals to natural-born creatures. It displays a quiet but profound melancholy, as seen when it watches wild Butterfree arriving at the mountain and remarks that those natural Pokémon, unlike itself and the clones, genuinely deserve the beautiful environment they inhabit. Despite its bitterness, Mewtwo is not cruel. It possesses a protective instinct toward the cloned Pokémon it created, and it steps in to prevent unnecessary conflict, such as when it stops the clone Pikachu from attacking Ash's Pikachu and calmly states that they are identical and that a fight would accomplish nothing.

Mewtwo's primary motivation in the special is the search for peace. It has already experienced the trauma of being used as a weapon by Giovanni and the pain of questioning its own right to exist. Now it hopes only to find a place where it and the cloned Pokémon can live undisturbed. However, this desire is repeatedly tested. Giovanni, who alone among humans retains his memory of Mewtwo, tracks it to Mount Quena and launches a military operation to recapture it. Mewtwo initially reacts with hesitation and uncertainty, unsure whether to flee or to stand and fight. Its motivation shifts as the story progresses: it begins to move from a stance of passive doubt to active protection of its family of clones, eventually sacrificing its own safety to shield them from Giovanni's forces.

The role Mewtwo plays in the story is that of the central figure around which the entire conflict revolves. It is both the hunted target and the reluctant hero. Throughout the special, Mewtwo observes the human characters—Ash, Misty, Brock, and the researcher Luna Carson—as they unknowingly draw closer to its hidden island. It saves a bus from a hurricane using its psychic powers, though it coldly explains to its clone companions that it acted only to prevent further human investigation. When Team Rocket agents capture Ash's Pikachu and the clone Pikachu prepares to attack, Mewtwo intervenes, asserting the equality of original and clone. Its most crucial action comes when Giovanni traps the cloned Pokémon in a force field and Mewtwo willingly enters the prison to protect them, enduring severe injury in the process. After being healed by the pure spring water at the mountain's summit, Mewtwo recovers its strength, obliterates Giovanni's equipment with a display of its full power, and teleports the entire spring and all present humans and Pokémon away from the conflict site. At the very end, Mewtwo thanks Ash and his friends sincerely for their help and then departs with all the cloned Pokémon to live as natural wild Pokémon elsewhere.

Key relationships in the story include Mewtwo's bond with the cloned Pikachu and cloned Meowth, who serve as its closest companions and who challenge its pessimism with their own questions about belonging. The clone Meowth in particular voices the idea that if wild Butterfree can see the moon in the same way, then cloned Pokémon should have the same right to the world. Mewtwo's relationship with Giovanni is defined by fear and defiance: Giovanni is the architect of its creation and the embodiment of human exploitation, and Mewtwo ultimately rejects him decisively. Its interaction with Ash is more nuanced. Ash does not try to catch or command Mewtwo; instead, he shows genuine concern and helps carry the injured Mewtwo to the healing spring. This act of selfless kindness contributes to Mewtwo's emotional development, allowing it to accept help and express gratitude—a marked shift from the defiance and isolation it displayed at the end of the first movie.

Mewtwo's development across the special is subtle but significant. It moves from a state of melancholy doubt and passive observation to one of decisive action and reluctant trust. Early on, it questions whether it and the clones even deserve their refuge; by the climax, it fights fiercely to protect that same refuge. It begins by keeping humans at a distance and ends by thanking them. This growth is not a complete transformation—Mewtwo remains wary of humanity and chooses to leave with its clones rather than integrate into the human world—but it represents an important step toward self-acceptance and the recognition that connection, even with humans, can have value.

Notable abilities of Mewtwo are extensive and formidable. It possesses extraordinary psychic powers, including telekinesis powerful enough to lift and move massive objects, create defensive barriers, and hurl opponents great distances. It can fly through the air under its own power. It communicates telepathically, allowing it to speak directly into the minds of both humans and Pokémon. It has the capacity to observe distant events through mental projection, as shown when it monitors the bus and the human travelers from afar. Its powers also extend to weather manipulation, demonstrated when it summons or redirects storms. It can teleport itself, other beings, and large geographical features such as an entire lake and spring. Additionally, Mewtwo has the ability to erase specific memories from the minds of humans, which it does to Team Rocket's agents at the conclusion of the story, ensuring that Giovanni's knowledge of its location is lost. Its physical regeneration is also notable: after being critically wounded by Giovanni's energy field, Mewtwo recovers completely after immersion in the healing spring water, restoring its full strength in a short time. These abilities, combined with its intelligence and growing emotional maturity, make Mewtwo a profoundly powerful presence and a character whose journey in this special is one of finding, through loss and sacrifice, a fragile but genuine peace.