When they first met, both Johanna and Katniss had a strong dislike for each other due to Johanna stripping in the elevator in front of her, Peeta, and Haymitch. However, once inside the arena, the two were thrown together into an alliance set up by Haymitch and the rebels of District 13. Even though the two were now allies, they still didn't trust each other. Katniss believes one of them will kill the other.
During the escape from the arena at the end of the 75th Hunger Games, Johanna 'attacked' Katniss for the purpose of removing a tracking device from her arm, then lead Brutus and Enobaria, the District 2 tributes, away from Katniss. As a result of this, Katniss began to hate Johanna, thinking she had meant to kill her until she realized Johanna had done and warmed to her.
After being rescued from Capitol's clutches in Mockingjay, Johanna and Katniss start to become friendly. Johanna, knowing that Katniss is indebted to her, begins to siphon off Katniss' morphling supply. As a result of the time spent together in the hospital, the two grow closer, and eventually become friends.
Once they are released from the hospital, Johanna and Katniss willingly move into a compartment in District 13 together, proving their friendship.
They train together to become part of a squad which would enable them to fight for the rebellion against the Capitol. When it comes to test their worth, Katniss passes, but Johanna has a breakdown and is sent back to the hospital. Before Katniss's departure, she visits Johanna in the hospital. Katniss gives her a small bundle that smells of pine to remind her of home. When she presents it, Johanna makes her promise to kill Snow and to make him pay for everything he's done.
Femslash ships within the Hunger Games fandom are not as prevalent as its het and occasional slash ships. Joniss has a notable, but small following.
There was some disappointment from fan as the film adaptions reduced Johanna's role, and did not show the pair bonding as much as is present in the books. Many fanworks take place around the time of, or after Mockingjay when Katniss and Johanna are recovering, leading to many hurt/comfort fics. Johanna's fear of water is also a common theme in these type of fanworks.
Joniss is the sixth most written ship within the fandom; Johanna's second most written and Katniss' third.