Jaiko is Gian's younger sister, who would have been Nobita's wife in the future had Doraemon not intervened. She appears in the very first chapter of the manga, even before the introduction of Gian. Her name Jaiko is usually considered a nickname, but Fujiko never gave her a real name.
An aspiring mangaka, Jaiko goes by her amateur Mangaka mangakastyle pen name Christine Goda (クリスチーネ 剛田 Kurisuchīne Gōda), and sometimes submits her manga to publishing companies for prizes. She mostly fails in these contest because her storytelling is still rough. After that when she decides to give up writing comic books, Gian's friends are asked/forced to cheer her up. She has a crush on Motayo Moto,a seventh grader in the school. She is sometimes referred to as Hana.
She loves to write comic books and draw. In the future she will be a famous writer with lots of copies of her comic books sold.
This is known because of an episode that Nobita asked Doraemon to help him, and he got a tool that has the ability to bring stuff that a person, in this case Nobita, will have in the future. He requested to the tool who would be standing next to him with wedding clothes, and Jaiko appeared. He got a quick depression and they travelled to the near Future, showing Nobita coming with Jaiko to an altar, and she was wearing a wedding dress. Nobita quickly fainted and he didn't realize that it wasn't a wedding! It was just an commemoration of millions of copies sold from Jaiko's recent success, a story related to wedding.
Doraemon told all of this to him when they got back to the present and guaranteed that she wouldn't be his wife, but Shizuka will. Nobita was so happy, but Doreamon quickly warned him that Shizuka would not marry with a boy that always has bad results, so he ran to Shizuka's house, crying, and promising he would be a good friend and have a good result in the next exam. Doraemon was on the roof and used the tool to see Nobita's next exam's result, and it was pretty good judging his reaction.