One in a set of three, with Dark Days and Assassination Days.
Well, after watching some of the latest episodes, and realizing that Assassination Classroom is about to come to an end, I decided I really needed to make some wallpapers for it. I really wanted to express the duality of the show, and how they combine in a rather cool manner, so that's why I made these three wallpapers.
This one represents the happy times, the fun times, the heartwarming times with Koro-sensei, the ones that will be cherished in the students' hearts forever. It's the one that closely reflects the warm, nostalgic feeling in the show's endings (example). In short, this wallpaper represents the happy times.