Cynthia (Shirona in the original Japanese version) is the Champion of the Sinnoh region, who debuted in Pokémon Diamond and Pokémon Pearl. She lives up to her reputation as the Champion, as she is no pushover. She trains very hard with her Pokémon, and managed to defeat all members of the Elite Four by doing so. She occasionally helps the player out in Pokémon Diamond and Pokémon Pearl. Her name comes from Synthesis, which means to combine different pieces together, and Cynthia combines multiple types of Pokémon.
Cynthia's very first appearance was in Pokémon Diamond and Pokémon Pearl, and later in the games' remake Pokémon Platinum. She first appears in Eterna City, when the player first enters the city. She gives the player some advice, but leaves shortly after. After Crasher Wake is defeated, Cynthia will be seen at Route 214. She is impressed with the players efforts, and how strong he/she is, and rewards the player with a SecretPotion. Cynthia tells the player to use this on the hoard of Psyduck, who are blocking the entrance to Celestic Town. She asks the player to go to Celestic Town, her home city, and tells the player to go give a gift to her grandmother. After the player does this, Cynthia will appear in the town, and thank the player for delivering the gift to her grandmother. Like most people in Celestic Town, Cynthia is very interested in the mythology behind the SinnohLegendary Pokémon. In fact, Cynthia commonly travels around Sinnoh to study more on these ancient creatures.
After the Team Galactic dilemma, the player eventually learns that Cynthia is, indeed, the Sinnoh Region Champion. Her abilities as a trainer are shown in this battle. Her Pokémon are all very powerful, all of which are above level 60. However, her powerhouse is Garchomp, which has several powerful attacks that can take away a massive amount of health in one attack. Although, after a long and arduous battle, the player comes out on top, and Cynthia and Professor Rowan deem the player as the new Champion. She can be battled again several times afterwards.
Cynthia then later made an actual appearance in Enter Champion Shirona!!. In this episode, Ash and the group were watching a battle between Cynthia and Lucian. Her Garchomp managed to easily defeat Lucian's Bronzong. Ash was determined to battle her. Meanwhile, Team Rocket, who were disguised as Ice Cream salesmen, actually got to meet Cynthia, who actually bought an Ice Cream from them. Ash and the gang then found Cynthia at the nearby ruins, which was just a little walk from Team Rocket's stand. She was studying about the ancient Pokémon Legends. However, when she notices a challenge from Ash's rival, Paul, she decides to battle him. She used her Garchomp, which managed to devastate Paul's Chimchar, Weavile, Murkrow, and Torterra with relative ease. However, Cynthia decided to look after Paul's Pokémon at the Pokémon Center, while at the same time, giving Ash and the gang tips on how to raise Pokémon. After they left the room to go outside for a little while, Team Rocket snuck in the building, and kidnapped Chimchar. However, Paul used his Ursaring to rescue Chimchar, which he then scolded for getting captured. Cynthia, however, cheered the young monkey Pokémon up, and told Paul that he has to show Pokémon compassion and respect. Paul, however, did not seem too interested in this advice. With all this done, Cynthia then decides to head off, and the group wave goodbye, while Paul hopes to get strong enough to defeat her.
Excluding the female playable character, Cynthia is the first female Champion to appear in a mainstream Pokémon game. She is also the second Champion to use a variety of Pokémon Types, instead of just one, the first being Blue.