Tuborochi; The Entropy of Orchestra

Strongly believed to be the bringer of the apocalypse that brought about the end of the Age of Humanity; Tuborochi is an anti-god (not devil) of the lands of Orchestra; Long ago, great psychomancers sealed it away in a prison of Tuba armor. Unfortunately; they only adapted and fused with this prison; growing even stronger. They are the secret, second phase of Tubasolator, and the true form of Queen Tuba.

https://www.youtube.com/watch?v=axusDzM-RC0

Tuborochi is arguably the hardest boss in the series, next to the Tuba Cat (aka the Real Tuba King), and the Woodwind Knight-Sorceress; due to the minimal movement space allowed and the sheer number of splash-damage projectiles raining in on the player; which makes it easy to lose their entire party.