Since its release in mid-October, Demon Slayer has generated ticket sales of ¥32.47bn [$313m], according to figures released on Monday by its distributors.
But it has seen cases surge in recent weeks, just as Demon Slayer came close to surpassing the ¥31.68bn grossed by the Oscar-winning Spirited Away.
Some fans, however, cautioned against making too strong a connection between an animated film and a lethal virus.
The film is in cinemas in Thailand and Taiwan, with dubbed and subtitled versions due for release in the US and Canada early next year.