This episode was made of win, a superb smorgasbord appropriate for celebrating Valentine's, what with a combination of a fantasy scene, some questions about the "class rules" answered, and a terrifying concluding scene echoing real-life school rampages (shades of Columbine and other tragedies).
If the novel were to be published in English, I'll not be surprised if it includes a foreword by Stephen King (who already praised Koshun Takami's Battle Royale).
And Kouichi X Mei... in the running as the best pairing of the season.
One more thing: the fantasy scene is, in a way, definitely a shoutout to Britney Spears'
Baby One More Time 
.