After Kelly began to review his life, he didn't want to end up spending his life like his father had done and began to think about what he should be doing. During a call, he met his former fighter friend and now med student, Jeff Clarke. Jeff asked him to come down to register on the bone marrow registry but Kelly saw it as unusual and brushed it off.
Jeff asked again and Kelly didn't go, but eventually he ended up coming to see Jeff, who showed him a sick woman in bed - Anna. He told her she was the reason he asked, because he's looking for bone marrows for her and he thought Kelly might be a match because of something he told him earlier. Kelly agrees.
Anna was undergoing chemotherapy and was happy to meet Anna. He got close to her but this was destroyed when Jeff told Kelly that her chemotherapy had made her too sick and she wouldn't be able to receive the bone marrow. He was deeply upset by this and spent his night at a bar that day, later being implicated in a hit and run by Chicago PD after Erin recognised his car at the scene but him being nowhere. He was cleared after the case was solved and Jeff told him that Anna could receive the bone marrow after all.
Kelly was told the time and he went to work like usual but was badly injured after he jumped out of a two-storey building to save himself from an explosion. He was badly injured and unconscious at the scene. Jeff treated him and told him he couldn't donate any longer, because his injury prevented him from receiving epidural. He insisted he could bear the pain but Sharon didn't let him but gave in after Kelly began calling other hospitals.
Severide donated his bone marrow in an extremely painful procedure as he had to be awake for the procedure, and Anna's life was saved in the process. She was thankful and they developed feelings for each other.
After Anna was discharged, she left to Springfield to continue working as a nurse at a hospital there. Kelly felt he was in love with her and considered a job as Battallion Chief there. However, she told him not to move because of her and after an emotional and hard case, he decided to stay in Chicago. Later on though, he tried inquiring about a job opening at Chicago Med for Anna, but Maggie told him the job was gone. Anna later surprised him in Death Trap and told him it was her who accepted the job.
She started getting homesick just a few days in her new city, especially after an upsetting day at the hospital, and told Kelly she was missing home in Babies and Fools. Kelly tried cheering her up by taking her out to ice skate, after which she said that she thought Chicago was a beautiful city.
However, in Take a Knee, Benny came to see Kelly and invited him and Anna to a dinner. She came late and only stayed for a few minutes, clearly upset about something, and got up abruptly and told him she had to leave. Kelly chased after her but she told him "goodbye" and left in a taxi.
In Carry Me, Anna's cancer was improving but she signed a DNR in case things worsened, which she knew they could. Kelly told the doctors not to listen to her but they said it was her choice. They start discussing one of the calls he tended to involving a widow who doesn't want to leave her burnt and damaged house, because Anna relates to it. She tells him to go work. Then during a call, Boden tells Kelly that there's been a change in Anna's condition and he needs to go to her straight away, which he does.
When Kelly gets to the hospital, doctors and Anna's father are with Anna, and the doctor tells him that her condition's worsened because of an infection, and there's nothing they can do. He sits by her side upset, and tells her she can still beat this. She tells him she loves him and he tells her to stop talking like that and that she's strong. She starts talking to him and her last words are "carry me".
She dies, and Kelly lashes out the doctors, telling them to save her. He cries and Anna's father stops him and hugs him to calm him down. He remains depressed over the next few days and even visits the old visit. He takes down important 'memories' from the house and tells her she can't keep the house, but she can 'carry' the important things with her. He misses her a lot, remaining unengaged with everyone else and ending up crying every time he remembers her.