• English / United States: Cissy
• Japanese / Japan: アツミ
• Japanese (Romanized) / Japan: Atsumi
• Japanese (TL) / Japan: Atsumi

Cissy is the Gym Leader on Mikan Island and Pokémon Trainers that defeat her earn the Coral-Eye Badge. Ash asked Tracey what the Mikan Gym Leader was like while walking to the gym and he replied that the Mikan Gym Leader "is one of the toughest trainers in the Orange Crew". Ash was psyched up when he heard him say that and could hardly wait to battle.

After hearing a ruckus outside the gym, Cissy introduced herself to Ash Ketchum and his friends and accepted Ash Ketchum's battle challenge. Ash Ketchum was a bit surprised that Cissy was the gym leader as he was expecting a guy trainer.

Cissy's Brother is her little brother who helps out during the gym battles by using the gyms remote control to activate certain parts of the gym as they are needed. She keeps him in check by watching over him so that he doesn't get into mischief while trying to skip doing his chores.

After Ash Ketchum was a bit confused by the setup of her gym match, Cissy explained to him that the Orange Island gyms do a lot more than just have Pokémon battles to win the badges. She explained that she had devised two challenges for this particular match which featured Water Pokémon. Her creativity and ingenuity was put on display during the challenges and it also showed how well she had trained her Pokémon. Cissy also pointed out that her Pokémon compete just like athletes do. The first challenge was a Water Gun accuracy challenge and the second challenge she devised was Pokémon Wave Ride race.

Tracey Sketchit seemed to have a bit of a crush on Cissy as he drew a picture of her on his sketchpad but Misty noticed it and made him blush a bit.