Zephyrus killed Icelord in the light novel in order to prove his loyalty to the Purple Order but the twist is that he wanted to join the Yellow Rebellion all along and personally started the war between Purple Order and Red Radicalists!!!
This way the City of Blue can live in peace against the brutal abuse they have been treated by the Noble Green as well as Pink Leaders!!! However, the battle was cut short when Prisoners of Black escaped banishment and wrecked havoc on the City of Blue.
Because the Red Radicalists cannot use their psychic powers since the Purple Order sealed their abilities, the Prisoners of Black were able to control the movements of everyone who lives in Ma Nga Cat using the Detrimental Destruction of Soul weapon that they created in the exiles. Fortunately, they are unable to seize the Yellow Rebellion due to their higher power which gave them the ability to access all the lands of Ma Nga Cat from anywhere they please.
In the end, Zephyrus transported every resident of the City of Blue, one by one, to the main base of Yellow Rebellion. He defeated the Prisoners of Black by destroying the core of Ma Nga Cat - the life force of this floating island - which causes the ground to burst into hellfire. This successfully decemated all of the Prisoners of Black in an instant, but that incineration took Zephyrus' life as well...
That day, Zephyrus was recognized as a hero. Rest in peace: Bringer of Harmony, King of Peace, Prince of Yellow.