Jedi Master Bastila Shan was discovered on the planet Talravin with a rare ability that manipulates the Force either influencing her allies or disheartening her foes with Battle Meditation. She was raised in the Jedi Order to become a skilled Jedi Knight, later on in her youth she had proven herself to be an asset to the Republic and the Jedi Order.
Bastila was the leader who led a strike team to capture Darth Revan which had succeeded with unexpected turn of events with Darth Malak took the title of Dark Lord of the Sith from him. After saving Revan, she was left to supervise and train him to become a Jedi once more after narrowly escaping Taris together with the help of T3-M4, Mission Vao, Zaalbar, Canderous Ordo and Carth Onasi, and thereafter later on in her journey with Revan she had also met HK47, Juhani and Jolee Bindo. Throughout her adventures with Revan, there was a lot of emotional hesitation and their bond that linked between her and Revan had led them in an all too familiar path where Basitla followed Revan's footsteps working closely with him to find the Rakatan Infinite Empire war factory called the Star Forge that was empowering Malak's Sith Empire. Bastila had trouble dealing with her emotions and soon realised she loved the man she had saved and grown to admire the man, stubborn as she was she couldn't defy the Jedi Code but after Revan and Bastila had bonded closely together their love had become their own strength.
However after Bastila was captured and turned to the dark side by Darth Malak, she had served as his apprentice and was force to confront the redeemed Revan. Revan and Bastila fought against each other in a deadly dual of fates on the final confrontation somewhere in the Star Forge where Bastila couldn't understand why Revan had loved her so much, she begged Revan to kill her but the one she saved had come back to return the favor. Using the bond they once share, and receited the Jedi Code with Revan and she was brought back to the light but asked Revan one last thing about their love for each other. Revan confessed that he loved her, and Bastila in turn said she would not be afraid to love him.
Kira Carsen was originally raised with the Sith Empire before she escaped and was later discovered by Jedi Master Bela Kiwiiks. She was brought into the Jedi Order and raised to become a Jedi, throughout her time spent with the Jedi Order she had become a skilled and yet talented individual in the Force. In retrospect Kira is similar to a Jedi Shadow or Jedi Sentinel with her knowledge of both the dark and the light side where she believed that the Jedi way is the right path for her.
Later on Master Orgus's Padawan that you play as through Star Wars The Old Republic (SWTOR) on the Jedi Knight storyline gets to have her come along for the journey and help you stop the Sith Emperor that you confront later on in the storyline. Kira's history with the Sith Empire would come back to haunt her but with the help of her new Jedi Master she would be emotionally drawn close to your decisions and choices. If you're playing as a male Jedi Knight on SWTOR, Kira could fall in love with you and her emotions towards you are very strong and her loyalty towards you would help you in the long term. Kira would no doubt look into the idea of marriage and having offsprings with you but with that being said, Bioware hasn't disclosed any information of possibly forming your family on the game yet aside from manually creating your own family tree.
Throughout the whole Jedi Knight storyline, both you and Kira are dedicated to stop the Sith and work together no matter what.