Episode 13.5

"The Common Cold" (風邪症候群) is an original video animation (OVA) episode for the Cells at Work! anime. It's based on the eleventh chapter of the manga, which has the same title.

Plot
At the Killer T Cell base, the Killer T Leader warns his men that cold season is just around the corner and instructs them on what to do when they spot one. As the Killer T Division proceed with their training regimen, a single Normal Cell proceeds with his replication process. Bored and dissatisfied by his day-to-day life, wishing for something new or exciting to occur, the NC hears a noise from outside his door. Outside, he finds a Rhinovirus by his house not knowing its identity as one. It calls NC over and the two sneak over to the Killer T base where they peep through a window through the base where Killer T instructs his subordinates to perform good hygiene. Enforcer Cell then hands Killer T a present addressed to him with no identification of who sent it. Elated, Killer T opens it, and a boxing glove springs out of it and punches him in the face knocking him over and onto the ground. Witnessing this, both NC and Rhinovirus burst out laughing blowing there cover cause Killer T and his division to chase after them. The two, however, manage to lose the Killer T Division in the Lymph Node Ducts.

Out of sight from the Killer T Division, the two then tail U-1146 who instantly senses the presence of the Rhinovirus. Because of this, they hide behind a corner. Playing with U-1146's antigen detection system, the Rhinovirus causes NC to burst out laughing blowing his cover behind the corner. Now aware of NC's presence, U-1146 warns NC of a rouge virus and volunteers to follow him as a bodyguard. Disconcerted by the offer, NC declines and rushes off in a panic leaving U-1146 left alone and perplexed. As the two run away again, NC states how much fun he's having and how he wants to perform more acts of mischief.

Afterward, the two break into a house and switch the salt and sugar jars. Hearing noise coming from the outside, they abscond. Helper T Cell and Regulatory T Cell then enter the house. When Helper T adds what he thinks is sugar to his tea from the bowl, he drinks it only to splurge it out due to its horridly salty taste. U-1146 arrives in the house asking if there was an antigen there, but Helper T denies there was someone there stating that someone switched the sugar with the salt.

Elsewhere, NC and Rhinovirus continue their mischievous prank spree on AE3803, Macrophage, and Basophil. Finally growing tired of their mischief making, NC states that he wishes to return home and continue his work. To that, Rhinovirus insinuates that he'd like to come over to his house as well and NC allows it, unaware that Rhinovirus had an ulterior motive.

In NC's house, the Rhinovirus shows his true colors as he tries to infect NC with his virus. He also summons his comrades and proliferates the area with his virus as well. All hope seemingly lost, NC is rescued by U-1146 and the Killer T Division who tracked the Rhinovirus through the traces of RNA left on the Punching Glove present he left for him. Thanks to effort of the Killer T Division, Macrophage, and B Cell, the Rhinoviruses are dealt with and sneezed out. NC is reprimanded for the trouble that he caused.

A few days pass and NC along with everyone involved with the prank spree enjoy either playing or watching a game of badminton. Forced into playing, Killer T plays a game as well and manages to send the birdie out of sight.

New characters

 * Rhinovirus

Returning characters

 * Killer T Cell (Squad Leader)
 * B Cell
 * Memory Cell
 * Enforcer Cell
 * U-1146
 * Helper T Cell
 * Regulatory T Cell
 * AE3803
 * Platelet (Leader)
 * Macrophage
 * U-4989
 * U-2001
 * U-2626
 * U-2048
 * Basophil