A lonely couple, who wanted a child, lived next to a walled garden belonging to an evil witch named Dame Gothel. The wife, experiencing cravings noticed a rapunzel plant. One night, her husband broke into the garden to get some for her, making a nice salad. It tasted so good that the wife longed for more. Her husband went a second time but Dame Gothel caught him and accused him of theft. He begged for mercy, and she agrees to be lenient, and allows him to take all he wants, on condition that the baby be given to her at birth. Dame Gothel took the child to raise as her own and names her Rapunzel after the plant her mother craved.
The child grew up to be the most beautiful child in the world with long golden hair that she never cut. She grew up atop a tower with only one room and no door, with only a window to see the world from. Every day she longed to leave the tower. When her "mother" the Dame visited her, she stood beneath the tower and Rapunzel let down her golden hair for her adopted mother to climb. However, these visits were months in-between each other and the lack of human contact did not help with her mental state.
One day, a prince rode through the forest and overheard Rapunzel singing from the tower. Entranced by her ethereal voice, he searched for her and discovered the tower, but is naturally unable to enter it. He returns often, due to her luring him with her beautiful singing, and one day he sees Dame Gothel visit, and thus learns how to gain access to Rapunzel. When Dame Gothel leaves, he bids Rapunzel let her hair down. When she does so, he climbs up, makes her acquaintance, and eventually asks her to marry him. Him being the best chance she had at escape, she agreed.
Together they planned a means of escape, wherein he will come each night, and bring Rapunzel a piece of silk, which she gradually weaved into a ladder. Before the plan can come to fruition, however, she foolishly gives the prince away by innocently saying that her dress is getting tight around her waist. In anger, Dame Gothel cut off Rapunzel's hair and threw her out of the tower into the wastelands to fend for herself. Without a safe exit, she fell onto the cold hard ground but she somehow survived the impact. There was great pain but at least she was finally free. It was worth it. When the prince calls that night, Dame Gothel lets the severed hair down to haul him up. To his horror, he finds himself staring at her instead of Rapunzel, who is nowhere to be found. When she tells him in anger that he will never see Rapunzel again, he leaps from the tower in despair and is blinded by the thorns below.
For months, he wandered through the wastelands of the country and eventually comes to the wilderness where Rapunzel with her hair regrown now lives with the twins she has given birth to, a boy and a girl. One day, as she sings, he hears her voice again, and they are reunited. When they fall into each other's arms, her tears immediately restore his sight. He leads her and their children to his kingdom. Here she lived happily ever after.
She neither knew what happened to Dame Gothel after she left the left the tower but she does not care, as far as she is concerned, she was an oppressor who existed only to cage her up, when she was free - in Rapunzel's mind - the Dame ceased to exist. She also does not care about the identity of her parents either and never wants to see then. Considering they essentially sold their newborn daughter for vegetables, this is more than justified.
Her Mad Enhancement has warped her personality. Here, Rapunzel's madness manifests as a fanatical obsession with the idea of freedom and as such she will turn on an "oppressor" as soon as she recognises one. She would be highly likely to turn on them as soon as possible, but would allow them to live if she judges them as an oppressor or not. However if the master shows the attitude of being "Master-Like" she would kill them on the spot with high spirits. Naturally, this makes her almost impossible to control.
If her Master was someone who "accidental got involved in the war", it would be fully possible for Rapunzel to fight at their side right until their defeat. She is particularly compatible with the likes of Sakura Matou as Sakura's battle was forced into her position and as such is a kindred spirit yearning for freedom. But it another matter entirely whether or not they would be able to achieve victory in the Holy Grail War.