Manatsu no Grey Goo

The sci-fi survival manga is about three high school friends: Manatsu Kurashiki, a member of the school's Kendo club; Tsumugi Midorikawa, who streams live videos of insects; and Ayano Yamaji, who likes reading about occult topics and urban legends. The three friends fail their exam, and they have to attend a supplementary class on the first day of summer. During their supplementary class, a helicopter from the Self-Defense Force suddenly lands on the school ground. The soldiers explain to their teacher that the town is in lockdown due to a nano machine attack. The three friends watching everything from their classroom are in shock when they see their teacher suddenly getting devoured by a huge number of ants.