Atma Weapon in Final Fantasy 6 (3). I have no idea why. I can't explain in detail the way you did. It just hit me out of nowhere. I was beating the bosses just fine until that guy on the floating continent completely halted my progress. Eventually I got help from a friend. We played the game in 2P mode where you can both fight battles together, and we stayed up all night eventually defeating it. Epic moments in JRPG gaming.