The Bugsters are the main antagonists of Kamen Rider Ex-Aid. They are viruses originating from glitches and enemies in video games seeking to wipe out humanity as revenge for killing them in video games for sport.
Most Bugster Viruses are spread through the Gashacon Bugvisor. Once it has infected its host, the Bugster Virus will grow once triggered by stress, weakening its victim's immune system in the process.
The Virus will eventually overtake its host, transforming the host into what is known as a Bugster Union. In this stage, the Bugster can only be defeated by a Level 1 Kamen Rider. Once the Union is defeated, the Bugster itself emerges while its former host begins to fade away. A Bugster infectee can be saved, however, by either defeating the Bugster that possessed it or completing the game which the Bugster originated from.
If the host fades away completely and dies, the Bugster will achieve its complete form. Bugsters who have achieved their complete forms can be brought back any time.
The Bugster virus originated from the Y2K Crisis of the year 2000. It was first discovered by a 14-year-old Kuroto Dan, who informed his father of it and later used it to infect a fan of his by the name of Emu Hojo.
In what came to be known as "Zero Day", a Bugster outbreak occurred when Bugsters emerged from 10 of the video games produced by Genm Corp. Unbeknownst to everyone, Kuroto Dan had triggered the outbreak as a way to gather data to make better games.
The outbreak killed four people in total, including Kuroto's mother Sakurako and Hiiro Kagami's girlfriend Saki Momose. Kuroto managed to avoid punishment for the crisis by pinning the entire thing on his father.
A second outbreak occurred 5 years later in the year 2016 and was sparked by a boy named Seiji Suyama being infected by the Salty Bugster. Though the Bugster was extracted and defeated, more Bugsters continued to emerge.
- Parado/Kamen Rider Para-DX
- Graphite Bugster
- Kuroto Dan/New Kuroto Dan
- Ren Amagasaki/Lovelica Bugster
- Salty Bugster
- Alhambra Bugster
- Revol Bugster
- Motors Bugster
- Gatton Bugster
- Vernier Bugster
- Kaiden Bugster
- Charlie Bugster