Manatsu no Grey Goo

Three high school students—Manatsu, a kendo club member; Tsumugi, who streams insect videos; and Ayano, interested in occult topics—fail an exam and must attend a summer supplementary class. On the first day, a military helicopter lands at the school, and soldiers inform the teacher that the town is under lockdown due to a nano machine threat. From their classroom, the three watch as their teacher is suddenly overwhelmed and consumed by a swarm of ants.