Starscourge Final Fantasy XV
A strange one this, as not only does it infect people, but also the world around them. It’s existed for millennia on Eos as a strain of malaria that’s not well understood, but reaches plague proportions during the events of FFXV, resulting in the shortening of day length and increase in aggressive daemons. It’s also nicknamed the ‘vanishing disease’ as eventually your body breaks down into a smoke-like miasma which then transitions into a daemon form. As the plague spreads and more miasma is created it absorbs the sun’s light, plunging the planet into an eternal night. While science doesn’t have a cure, the royal Lucius family does, although it takes Noctis sacrificing his own life to do it and restore light to the world.