Four is Sayori
Seven is Yuri
Two is Natsuki
Six is Monika
This is a crossover AU I made and things. Four wants you to join a club as you join the numbers have been falling in love. But things have been taking a turn. 
Day 1: Four runs late and after school she wants you to join a club. Six,Seven and Two were happy to see you join too
Day 2: Four gets a bit depressed and goes missing 
Day 3: Seven brings a knife to school looks like losing her sanity and Two dies
Day 4: Just Six