Misty, known as Kasumi in Japan, is a fictional character in the Pokémon franchise. She has appeared as a Gym Leader in the Pokémon video games, several seasons of the Pokémon anime, The Electric Tale of Pikachu manga, the Ash & Pikachu manga, toys, books and other media.

Misty is 10 years old at the start of the series. She has a slight inferiority complex, especially due to the fact that her three sisters Daisy, Lily and Violet do not think much of her, claiming that there are only three Sensational Sisters (the name under which they perform synchronized swimming) and one "runt." This complex diminishes over time as Misty grows much closer to Daisy (the most motherly and girly of the sisters). They are the ones who usually take care of the issues related to the Cerulean Gym, although it was Misty who battled Ash when he was battling for his Cascade Badge there.

In the early episodes, Misty is depicted as having a wicked temper, spoiled attitude, stubborn temperament, and little patience. As the series progresses, however, she gradually shows herself to be kind and sensible. She reins in Brock when he becomes enamored with cute girls, often pulling him away by the ear. (This role was later taken by Max and, briefly, Brock's Bonsly during seasons 6-9, and then by Brock's Croagunk in season 10.) She has a slight rivalry with Ash in some episodes. She is also terrified of Bug-type Pokémon and dislikes carrots and peppers. She loves Water-type Pokemon and being barefoot.

Misty aims to be a world-class Water-type Pokémon trainer despite her sisters' ridicule. Her well trained Pokémon reflect her aspiration. She admires the Ice-type trainer Lorelei. She is a good friend of Sakura, a young girl who also has older sisters who treat her like a child.

When a Pokémon egg that Ash had been carrying in his backpack hatches, Togepi is born. Since Togepi had already chosen her as its "mother," Misty ended up keeping it, even though Ash had won the Pokémon in a mini-tournament involving him, Misty, Brock, and Meowth. She takes on a motherly role to Togepi, being virtually inseparable from it throughout future seasons.

Although Misty is the leader of the Cerulean Gym in the games, she left the Gym to her three older sisters prior to traveling with Ash in the animated series. She first came across Ash when she accidentally fished him and his Pikachu out of a river while fishing for water Pokémon. Soon after this incident, Ash "borrowed" her bike, attempting to flee from a flock of wild Spearow. The bike was later charred to a crisp by a Thundershock from Pikachu. Misty used the destroyed bike as an excuse to become Ash's friend, telling him she wouldn't leave him alone until he replaced the bike. However, this plot point later became moot, as Misty actually forgot why she started traveling with him in the first place.

After retrieving her bike at the end of the Johto League Silver Conference, she returns to Cerulean Gym and resumes her duties as the Gym Leader while her sisters leave for a cruise around the world. As such, she is not featured as a main part of the Advanced Generation series and only appears in five episodes and in The Mastermind of Mirage Pokémon, a 10th Anniversary special episode event. However, she is often a central character in Pokémon Chronicles. In one of her few appearances in the Advanced Generation series, her Togepi evolves into Togetic. Misty releases Togetic after it chooses to stay behind to defend the Mirage Kingdom. After Ash finishes competing in the Hoenn League, he returns home to Pallet Town to find Misty waiting for him. However, she isn't the only one to rejoin Ash, as May, Max, and Brock join him as well for the Battle Frontier challenges. She remains in his team for three episodes, and shortly after returns to her gym.