Aerith

Aerith is a character who lives in Traverse Town in Kingdom Hearts and Kingdom Hearts: Chain of Memories and Hollow Bastion/Radiant Garden in Kingdom Hearts II. Like most of Sora's allies, she originates from the Final Fantasy series. Aerith is voiced by Mandy Moore in Kingdom Hearts, Mena Suvari in Kingdom Hearts II, and Maaya Sakamoto in the Japanese versions of both games.

An ally of Leon and Yuffie, Aerith is one of the three core Final Fantasy characters of the series, and takes an active support role with them in the defense of Hollow Bastion in Kingdom Hearts II. She also plays a part in Cloud's story, though does not directly assist him as she does her other allies.

Kingdom Hearts
''She lost her home to the Heartless at a very young age. Beneath her gentle disposition lies a strong will and a firm sense of duty. Many are naturally drawn to her. Aerith works with Leon and Yuffie to learn more about the Heartless and the "key".''

"Final Fantasy VII"

Kingdom Hearts: Chain of Memories
''A young woman who fought the Heartless. Her calm demeanor hides an unbreakable will.''

Aerith also has a mysterious sense of truth, and is aware that Traverse Town and its inhabitants are a figment of Sora's memory.

Kingdom Hearts II
Final Fantasy VII

''A young woman whose quiet eyes belie an unbreakable will. Like Leon, she met Sora while living away from her hometown, and helped him now and then on his journey.''

Now Aerith works with Leon and Yuffie to restore the town to its past splendor.

Kingdom Hearts
Aerith is encountered by Donald and Goofy on the first trip to Traverse Town, where she explains the nature of Ansem's Report, as well as the Keyblade to them. She had a few more appearances along with Leon and Yuffie. Later, she showed up in Hollow Bastion after Ansem disappeared, and spends her time studying the Heartless's research in Hollow Bastion's library. If you talk to her a multiple number of times she will give you the missing Ansem Reports that Maleficent had and Curaga, the strongest cure spell in the game.

In a scene exclusive to Kingdom Hearts Final Mix, Aerith reveals she was aware Cloud was at Olympus Coliseum, and mentions Cloud seeking Sephiroth when she discusses the matter with Sora.

During the end credits she is seen with Leon and Yuffie inside the Hollow Bastion library, and is the first to greet Cloud when Cid returns him to their world.

Kingdom Hearts: Chain of Memories
An image of Aerith appears, along with Leon, Cid, and Yuffie, in the memory-based Traverse Town in Castle Oblivion. At first, she, like the other characters, expresses disbelief that she seems to know Sora despite not remembering him. After speaking with Sora one-to-one, however, she comes to realize that she is just a projection based off his memory of her. She and Maleficent, in Riku's Reverse/Rebirth, are the only ones to realize this. She tells Sora to be on his guard. However, it seems that Sora is the only one who can see her in the first place (Donald and Goofy assume that she had gone back with Leon and company already).

Kingdom Hearts II
Aerith is a member of the Hollow Bastion Restoration Committee. In Kingdom Hearts II, she wears a modified version of her Before Crisis outfit, though wearing a pink skirt instead of green. She helps during the invasion of Hollow Bastion by healing Yuffie and presumably continues to aid other characters or fight against the Heartless. Aerith assisted Sora later in the game during his movement against the Master Control Program by downloading the deletion program.

In her last appearance of the game, during the ending credits, she is seen sitting on a ledge and looking up towards the Radiant Garden's sky, possibly wondering what happened to Cloud and Sephiroth after their fight at the Dark Depths (assuming the player has completed the sidequest involving them). Throughout the story she encourages Cloud to do what he must to fulfill his goals. Aerith is sure that Cloud will find his light, which will lead the way back to her.

Abilities
Aerith, unlike most other Final Fantasy characters, has not yet been either a combat ally or opponent for Sora, or seen to engage directly in battle against an opponent, and so her combat abilities, if any, are unknown. Aerith does seem able to cast magic, however, as she casts a Curaga spell on Yuffie during the invasion of Hollow Bastion, and also upgrades Sora's Cure spell. This seems roughly in-line with her Limit breaks, centered around healing, in Final Fantasy VII. Despite never physically being seen in battle, she is implied at one point to have held off waves of Heartless spawned by the MCP (coldly spurning Leon's concern over whether she would be able to handle it by herself), hinting that she does possess combat abilities.

She carries no visible weapons at any time, unlike most other Final Fantasy characters, but it would likely be a quarterstaff as per her original incarnation.

Trivia
Aerith
 * Aerith is called "Aeris" in Final Fantasy VII due a mistranslation. She is named "Aerith" in all other games and media including the Kingdom Hearts series.
 * Aerith's clothing in Kingdom Hearts and Kingdom Hearts: Chain of Memories is very similar to the one she wears in Final Fantasy VII, though without her jacket. A belt is also added but other then that, no dramatic changes have occurred. In Kingdom Hearts II however, her outfit undergoes a major change and resembles the one she wears in Before Crisis, only to be red instead of green.
 * Though Mena Suvari is carried over as the voice of Aerith in her role in Final Fantasy VII: Advent Children, due to negative reactions, she is later voiced by Andrea Bowen in Crisis Core -Final Fantasy VII-, a performance which was better received, and will likely voice Aerith in subsequent incarnations of the character, including her Kingdom Hearts series self.