High School☆Survival

One day after school. The protagonist, a second year student at Umenoki High School and a member of the student council, was attending a meeting with three other student council members to discuss the upcoming school festival,They were having a meeting about the next cultural festival. The meeting was heated, but the day was getting late, so it was decided that they would postpone the decision until the next meeting. The meeting broke up and everyone was about to go home when a scream came from outside Panicked, they look outside and see "something" in the form of human attacking the students. The protagonist and three other members of the student council are forced to stay in the school until help arrives... The four, work together to secure lifelines and find out the identity of the "something" outside and its cause. Will they survive until help arrives? And what is the cause of all this?