Yuri is a friendly girl, she currently attends the junior high school attached to the Tokyo Central Campus, a new style educational facility set up by Agency, the regulatory centre for Viruses and Programs. Yuri's best friends are Ayumi and Kuya, her classmates.

Yuri suffers a little celebrity in her school due to her brother Yoh and his program Yuki. She is sometimes a bit ashamed of this, since her studies in modern history and technology are not the most competent.

With the appearance of Virus, Yuri's ordinary life is turned upside down and she joins the elite forces battling viruses to defend Tokyo.

Virus is a mysterious boy that appears through Yuri's computer, an ability that has an as of yet unknown origin. He possesses the distinctive ears of an earlier model Program Shell, yet the Agency finds no records of his creation or indeed his model type and number.

Virus seems to suffer from a program form of amnesia and cannot remember anything prior to his appearance, but at times show innate abilities as a very capable Anti-virus Program.

A boy plagued with emptiness yet owning a soul of his own, Virus joins forces with Yuri. Indeed, it is as if he was meant for her...

Yoh is rather popular at his school, the senior high situated in the same campus as Yuri's school. He is athletic, funny, and altogether too mean to some of his peers. He loves to tease people, but does so without actually being malicious. Yoh's favourite spot in school is the gardens, but only when Yuki is there too.

Yoh and Yuki make up one of the elite partnerships in the Virus Hunting business, they are contracted by the government to battle infestations and manifestations of viruses, worms and all malevolent program activity in Tokyo. They are not the only group, but the two prove to be the most efficient. Their group name is the "Y's Winter".

Yoh also has his own fanclub, a group of screaming fangirls that calls themselves the Yohtaku...

Yuki is a cool and collected man, he was produced especially for the anti-virus effort, and as such, is highly specialized in all defence and attach abilities a program could have. Yuki is partnered to Yoh, and the two are almost unchallenged in their supremacy in their field.

Unlike Yoh, Yuki prefers solitude and silence. His favourite thing to do each day is to curl up with a good book in the shade and doze when he gets tired. Yuki is often looked upon by the rest of his classmates as Yoh's caretaker, the one to step in if Yoh does anything too stupid.

Yuki and Yoh seem to have some hidden agreement about Yuri and her new partner Virus, but what it is will not be revealed yet. There is also speculation that the two's relationship is beyond 'just friends', but Yuki in particular makes no comments to that effect.

Aruita has just appeared in the series, and not much is known about her except that she is a virus that has somehow infiltrated the Agency and is currently working for them.

Garan's leader seems to be keeping something from him, and from what we've seen so far he seems eager to prove himself and gain favour...

A mysterious man that appears briefly in Issue 2. He seems to be leading a group of Viruses that wish to change the world...

A figure that is seen only for a moment in Issue 3. Someone that releases Virus' power and asks Yuri her reasons for wanting to fight. Seems to be an ally...