this hits hard when you'll relate to these lyrics in a year. im gonna miss my friends/classmates from school so bad. love them so much and i hope we can meet again. :) this song basically has nostalgia, melancholy and sadness that emerged from joy INGRAINED into it. it's been years since i watched this anime, and now i can actually relate to the lyrics.
First I watched this anime on RU-vid, when I was around 15 year old, as many of students of E-class. That time it was airing, I guess. Then I abandoned it for 8 years, and now, after listening to this opening and "Question", I returned to watch it again. Finishing it feels like I finally graduated in spiritual way. It is special, that I'm around the same year as the students of E-class. So nostalgic song, miss my high school years and want to live through again, even if these years weren't good enough as I wished...
The fourth and final opening theme of Assassination Classroom, "Bye Bye Yesterday", is the most melancholy, yet thrilling, song in the world of Japanese anime of the "Anison" genre. How I wish I was part of the Assassin 3-E class at Kunugigaoka Middle School. Also being able to participate in the assassination/rescue of Koro-sensei. Truly being part of that world, as if I were really one of those characters, would make me very happy, especially if I managed to get engaged either to Yada Toka or to Kurahashi Hinano, for the simple fact that the other girls were already all engaged or engaged to the other male characters in the anime series. Furthermore, this type of theme song is also my favorite of: "Assassination Classroom". 
I enjoy how the majority of the song is sung in groups (Karma Yuma and Hiroto vs Kaede and Nagisa) and they only have solo lines in the bridge. Shows how united they are, and fits the theme of the song
Glad to see people still remember this. This came out when I was still in elementary school. I graduated this year. My school life wasn't as... interesting as 3-E's, most of my classmates won't even remember me after a year and honestly all of them were kind of assholes. This anime gives me something I'll never have, and I'll keep coming back to it.
