Alyssa Breslin is a minor character from Trauma Team, who is a recurring character in Naomi's storyline.
Alyssa shows up at Naomi Kimishima's workplace, requesting for Naomi to help treat her cat, Chloe. While Naomi reluctantly entertains Alyssa during her frequent visits, she eventually warms up to her.
When Naomi was investigating the murder of Alma and Abagail Parker, Alyssa unknowningly assisted in finding the murder weapon, which was lodged inside of a clock. When the clock begun to play a song, Alyssa said, "I'm sorry, but this clock is broken! I know how this song goes, and it goes all weird at this one part!" Little Guy then proceeds to open up the clock at Naomi's request, revealing the murder weapon inside.
When Naomi was investigating a criminal known as "The Raging Bomber", she receives a package with a teddy bear and a note, seemingly from Gabriel Cunningham. Shortly after signing the package, she finds carbon dust on her hand (which was present on previous victims, the Revolutionary and Aidan Posner), and realizes that the teddy bear is a bomb. However, Alyssa had already maliciously stolen the teddy bear and took returned to her home when the bomb inside detonated, injuring her, killing her family and burning down her house.
As Alyssa is sent to Resurgam First Care for treatment, Naomi's phone goes off, signifying Alyssa's death. As she begs for Alyssa to stay alive, CR-S01 proceeds to operate on Alyssa, saving her life despite the unfavourable conditions in the old ward.
As there were no surviving relatives after the explosion, Naomi adopts Alyssa as she is recovering in the hospital, planning to pass responsibility on to the FBI once Naomi dies from her genetic disease. However, after the Twisted Rosalia is treated, it is discovered that Naomi is cured of her genetic disease, leaving her able to continue raising Alyssa.
- In Chapter 7 in Naomi's story, when Little Guy said that 'Once she recovers, she'll be sent to an orphanage', this suggested that Alyssa used to have parents, but they got killed in the explosion. This fully explains why Naomi is adopting her aside from the fact she doesn't have any relatives.
- Along with Jacob Tillman, Alyssa is one of the very few characters to appear in Patient Zero who did not get infected with the Rosalia Virus.