Krillin & C-18

Their Relationship
Krillin and 18 first met when Dr. Gero was defeated by the Z Fighters and he desperately released 17 and 18 as a way to kill the Z Fighters but the two androids instead betrayed Dr. Gero and killed him. Three years prior to this meeting, all the Z Fighters were visited by Future Trunks, who told them that 17 and 18 would appear and cause massive havoc around the world that would result in the death of all the Z Fighters and a third of the world population. Due to this, Krillin went through intense training to prepare for the upcoming battle but secretly felt afraid of facing the androids. When they finally meet, Krillin was afraid of her and 18 initially didn't pay attention to him, as she was more interested in fighting Vegeta and hunting down Goku to kill him. However before she left to find Goku, she shocked Krillin by kissing him on the cheek as a goodbye token. Krillin remained perplexed by the kiss and began questioning whether or not she was truly evil. Bulma created a detonator to shut down the androids and instructed Krillin to do it. Krillin agreed to the task but when the moment came, he had doubts because he was haunted by the kiss and no longer believed she was evil, and thus didn't deserve to die.Krillin ultimately decided he had fallen in love with her and destroyed the detonator, and asked 18 to let him help her and 16 escape after Cell absorbed 17. However Cell absorbed 18 and formed the Cell Games to fight the Z Fighters. When Cell was losing to Gohan, 18 was freed from Cell and Krillin immediately took care of her, despite the protests of the other Z Fighters. After Cell was defeated, 18 was ready to leave and refused to acknowledge Krillin, but she secretly stayed as Shenron was summoned and Krillin wished for the bomb inside 18 to be removed so she can be more human-like. When questioned for this, Krillin admits his feelings for her but believed she and 17 were a couple. 18 shouted 17 is her twin brother and she is not interested in Krillin but she thanked him for saving her before leaving. Despite this, Krillin still hoped there was a chance 18 harbored an interest in him.

Over the next four years, Krillin continued to pursue 18 romantically until she finally agreed to marry him. A year after their marriage, their daughter, Marron, is born. Krillin retires from martial arts after settling down and spends time with his family. 18 also settles down and devotes herself to raising her daughter, as she states nothing can make her more happy than her child. As a married couple, they have a good relationship and appear devoted to their family. 18 tends to downgrade Krillin as a fighter because she is much stronger than him but she is also proud of him for giving his best and admires his persistence.

Trivia

 * Although 18 kissed Krillin suddenly to tease him when they met, that is what set the stage for Krillin to pursue her.
 * In Future Trunks' timeline, 18 killed Krillin without hesitation, and thus they never married and had a family.