It’s not that song, it’s a song that plays during the climax of End of Evangelion and has very strong themes of suicide and loss, played over an upbeat, lively tune. Just imagine these lyrics over something reminiscent of a Beatles song circa Sgt. Pepper’s Lonely Hearts Club Band:

*I know, I know I’ve let you downz

I’ve been a fool to myself

I thought that I could

live for no one else

But now through all the hurt and pain

It’s time for me to respect

the ones you love

mean more than anything

So with sadness in my heart

(I) feel the best thing I could do

is end it all

and leave forever

what’s done is done it feels so bad

what once was happy now is sad

I’ll never love again

my world is ending

It’s one of my favorite scenes in animation, just because of how utterly fucked up everything is and how many layers there are to everything