King Matthias's late father, who appears as a ghost throughout the story. Like his grandson, Prince Meech, he's kindhearted and peaceful, and wants to heal others. He doesn't approve of his son's disease-causing actions, but tries to comfort him whenever the latter needs it. He also provides Meech of some helpful advice regarding trying to befriend cells.

Loki is pansexual.

A Bifidobacterium bifidum cell.
She's the leader of a B. bifidum tribe. Given they're not an infectable target, Sapphire is neutral toward SARS-CoV-2 at first. But something happens which causes her to become hostile with the virus and join the immune system in the battle against it.

The virion who jumped from animal to human, and infected the very first human. He's the original 2019 Wuhan wild-type and King Matthias's 7th great-grandfather. Haojiao has a brief appearance in Virus Attack, but he plays the main role in The Howling Crown.

A devil figure in Noxsolisan mythology. His name is pronounced as dee-BEE-yug.
He has no true form, but instead appears differently in the imagination of every individual virion. Some think he has horns, why others think he has not. Some also imagine him with wings, and some think he's the size of a regular virion, why others think he's huge. There are virions who think he'd rather appear in the form of a completely normal looking virion. Though, he's almost always said to have a voice as loud and deep as thunder.

He appears to King Matthias in a nightmare scene. Because it is a dream, Dbiyg changes shape many times, but eventually settles as a distorted version of Prince Scratcher. He also moves around in a very unnatural way. King Matthias always imagined Dbiyg as a scary, huge skull-faced, skeletal creature with horns. Though, there's a specific reason to why Dbiyg takes on the form of his son in this nightmare.

*The liquid dripping from Dbiyg's nose and mouth is blood. It should be green, but because King Matthias's species can't see green, it appears as a dirty yellowish color to him.