Lyric discussion by MDramamineM 

Cover art for Dropla  lyrics by Youth Lagoon

Trevor, the songwriter, told me it's about his grandma dying, how he was really close with her, and being in denial that she was actually going, which is the reason for all of the "you'll never die" repetition and desperation in the song.

the spirit building a new brain is likely a reference to ephesians 4:23/romans 12:2, i believe.