Kamen Rider Neo-Heisei Part 4: Ex-Aid

From the introduction:

In the year 2011, there was an outbreak of a new disease: The Bugster Virus. Spawned from computer data, this virus spawns a ‘Bugster’ - a video game enemy or character made real - from the host, eventually causing the host to disappear from existence to fuel the Bugster’s existence and letting them become ‘complete’. The outbreak was eventually halted, and the CEO of Genm Corporation, the one said to be responsible for this ‘Zero Day’, was arrested and jailed. While the event never reached the eyes and ears of the public, there were many who had died as a result of Zero Day, carving the legacy and existence of the Bugster Virus into the medical community.