Fujisawa Yuki manga
It’s February, and it still hasn’t snowed. Kanon’s father is going on a business trip and might be getting too friendly with a subordinate, which Kanon doesn’t approve of so soon after her mother’s death. Her little brother collects insects, but they’re dying off. And it turns out that this die off is the first of many a plague to come down. First it’s the insects. Then it’s the rats, looking for a new food source. Then it gets bad…
A level seven earthquake hit the the Kanto area at 4:55am. 10 survivors are stuck underground on the subway; 2 salary-men, a couple with a young son, an old couple, a calm and collective girl, the subway engineer, and their appointed leader, a man who's never worked to overcome the obstacles in life. How will they escape? What can they do to escape? "It's amazing what people will do to stay alive."
There was a fire. Kousei lost his mother, his father and his precious little sister, Sanae. One month later he woke up to find himself in a hospital and was moved to pediatrics where he could share a room with other boys his age. Professor Kimishiro is loved and respected by his students, but disliked by faculty and administration. He's pushed from his classroom by university politics and takes a team to the jungles of the Amazon in search of new medicines and perhaps a chance to gain back his reputation amongst those with influence back home. Instead of cures, his team stumbles upon a lost temple in the jungle, a place the village guides claim to be 'The House of the God of the Black Death'. What are the temple's secrets, and can any man, let alone a mere boy, survive the plague of an angry God?
The basic idea is that man is having a hard time finding food and getting rid of their trash, so science comes up with a bio-engineered animal that survives by eating trash, and is then killed to feed humanity. You can guess what may happen if a self-replicating, endlessly hungry killing machine got loose in Tokyo.